Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 6179 insertions, 0 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
new file mode 100644
index 0000000000..f232cf56fa
--- /dev/null
+++ b/kernel/trace/ring_buffer.c
@@ -0,0 +1,6179 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generic ring buffer
+ *
+ * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
+ */
+#include <linux/trace_recursion.h>
+#include <linux/trace_events.h>
+#include <linux/ring_buffer.h>
+#include <linux/trace_clock.h>
+#include <linux/sched/clock.h>
+#include <linux/trace_seq.h>
+#include <linux/spinlock.h>
+#include <linux/irq_work.h>
+#include <linux/security.h>
+#include <linux/uaccess.h>
+#include <linux/hardirq.h>
+#include <linux/kthread.h>	/* for self test */
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/mutex.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/hash.h>
+#include <linux/list.h>
+#include <linux/cpu.h>
+#include <linux/oom.h>
+
+#include <asm/local.h>
+
+/*
+ * The "absolute" timestamp in the buffer is only 59 bits.
+ * If a clock has the 5 MSBs set, it needs to be saved and
+ * reinserted.
+ */
+#define TS_MSB		(0xf8ULL << 56)
+#define ABS_TS_MASK	(~TS_MSB)
+
+static void update_pages_handler(struct work_struct *work);
+
+/*
+ * The ring buffer header is special. We must manually up keep it.
+ */
+int ring_buffer_print_entry_header(struct trace_seq *s)
+{
+	trace_seq_puts(s, "# compressed entry header\n");
+	trace_seq_puts(s, "\ttype_len    :    5 bits\n");
+	trace_seq_puts(s, "\ttime_delta  :   27 bits\n");
+	trace_seq_puts(s, "\tarray       :   32 bits\n");
+	trace_seq_putc(s, '\n');
+	trace_seq_printf(s, "\tpadding     : type == %d\n",
+			 RINGBUF_TYPE_PADDING);
+	trace_seq_printf(s, "\ttime_extend : type == %d\n",
+			 RINGBUF_TYPE_TIME_EXTEND);
+	trace_seq_printf(s, "\ttime_stamp : type == %d\n",
+			 RINGBUF_TYPE_TIME_STAMP);
+	trace_seq_printf(s, "\tdata max type_len  == %d\n",
+			 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
+
+	return !trace_seq_has_overflowed(s);
+}
+
+/*
+ * The ring buffer is made up of a list of pages. A separate list of pages is
+ * allocated for each CPU. A writer may only write to a buffer that is
+ * associated with the CPU it is currently executing on.  A reader may read
+ * from any per cpu buffer.
+ *
+ * The reader is special. For each per cpu buffer, the reader has its own
+ * reader page. When a reader has read the entire reader page, this reader
+ * page is swapped with another page in the ring buffer.
+ *
+ * Now, as long as the writer is off the reader page, the reader can do what
+ * ever it wants with that page. The writer will never write to that page
+ * again (as long as it is out of the ring buffer).
+ *
+ * Here's some silly ASCII art.
+ *
+ *   +------+
+ *   |reader|          RING BUFFER
+ *   |page  |
+ *   +------+        +---+   +---+   +---+
+ *                   |   |-->|   |-->|   |
+ *                   +---+   +---+   +---+
+ *                     ^               |
+ *                     |               |
+ *                     +---------------+
+ *
+ *
+ *   +------+
+ *   |reader|          RING BUFFER
+ *   |page  |------------------v
+ *   +------+        +---+   +---+   +---+
+ *                   |   |-->|   |-->|   |
+ *                   +---+   +---+   +---+
+ *                     ^               |
+ *                     |               |
+ *                     +---------------+
+ *
+ *
+ *   +------+
+ *   |reader|          RING BUFFER
+ *   |page  |------------------v
+ *   +------+        +---+   +---+   +---+
+ *      ^            |   |-->|   |-->|   |
+ *      |            +---+   +---+   +---+
+ *      |                              |
+ *      |                              |
+ *      +------------------------------+
+ *
+ *
+ *   +------+
+ *   |buffer|          RING BUFFER
+ *   |page  |------------------v
+ *   +------+        +---+   +---+   +---+
+ *      ^            |   |   |   |-->|   |
+ *      |   New      +---+   +---+   +---+
+ *      |  Reader------^               |
+ *      |   page                       |
+ *      +------------------------------+
+ *
+ *
+ * After we make this swap, the reader can hand this page off to the splice
+ * code and be done with it. It can even allocate a new page if it needs to
+ * and swap that into the ring buffer.
+ *
+ * We will be using cmpxchg soon to make all this lockless.
+ *
+ */
+
+/* Used for individual buffers (after the counter) */
+#define RB_BUFFER_OFF		(1 << 20)
+
+#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
+
+#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
+#define RB_ALIGNMENT		4U
+#define RB_MAX_SMALL_DATA	(RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
+#define RB_EVNT_MIN_SIZE	8U	/* two 32bit words */
+
+#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
+# define RB_FORCE_8BYTE_ALIGNMENT	0
+# define RB_ARCH_ALIGNMENT		RB_ALIGNMENT
+#else
+# define RB_FORCE_8BYTE_ALIGNMENT	1
+# define RB_ARCH_ALIGNMENT		8U
+#endif
+
+#define RB_ALIGN_DATA		__aligned(RB_ARCH_ALIGNMENT)
+
+/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
+#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
+
+enum {
+	RB_LEN_TIME_EXTEND = 8,
+	RB_LEN_TIME_STAMP =  8,
+};
+
+#define skip_time_extend(event) \
+	((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
+
+#define extended_time(event) \
+	(event->type_len >= RINGBUF_TYPE_TIME_EXTEND)
+
+static inline bool rb_null_event(struct ring_buffer_event *event)
+{
+	return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
+}
+
+static void rb_event_set_padding(struct ring_buffer_event *event)
+{
+	/* padding has a NULL time_delta */
+	event->type_len = RINGBUF_TYPE_PADDING;
+	event->time_delta = 0;
+}
+
+static unsigned
+rb_event_data_length(struct ring_buffer_event *event)
+{
+	unsigned length;
+
+	if (event->type_len)
+		length = event->type_len * RB_ALIGNMENT;
+	else
+		length = event->array[0];
+	return length + RB_EVNT_HDR_SIZE;
+}
+
+/*
+ * Return the length of the given event. Will return
+ * the length of the time extend if the event is a
+ * time extend.
+ */
+static inline unsigned
+rb_event_length(struct ring_buffer_event *event)
+{
+	switch (event->type_len) {
+	case RINGBUF_TYPE_PADDING:
+		if (rb_null_event(event))
+			/* undefined */
+			return -1;
+		return  event->array[0] + RB_EVNT_HDR_SIZE;
+
+	case RINGBUF_TYPE_TIME_EXTEND:
+		return RB_LEN_TIME_EXTEND;
+
+	case RINGBUF_TYPE_TIME_STAMP:
+		return RB_LEN_TIME_STAMP;
+
+	case RINGBUF_TYPE_DATA:
+		return rb_event_data_length(event);
+	default:
+		WARN_ON_ONCE(1);
+	}
+	/* not hit */
+	return 0;
+}
+
+/*
+ * Return total length of time extend and data,
+ *   or just the event length for all other events.
+ */
+static inline unsigned
+rb_event_ts_length(struct ring_buffer_event *event)
+{
+	unsigned len = 0;
+
+	if (extended_time(event)) {
+		/* time extends include the data event after it */
+		len = RB_LEN_TIME_EXTEND;
+		event = skip_time_extend(event);
+	}
+	return len + rb_event_length(event);
+}
+
+/**
+ * ring_buffer_event_length - return the length of the event
+ * @event: the event to get the length of
+ *
+ * Returns the size of the data load of a data event.
+ * If the event is something other than a data event, it
+ * returns the size of the event itself. With the exception
+ * of a TIME EXTEND, where it still returns the size of the
+ * data load of the data event after it.
+ */
+unsigned ring_buffer_event_length(struct ring_buffer_event *event)
+{
+	unsigned length;
+
+	if (extended_time(event))
+		event = skip_time_extend(event);
+
+	length = rb_event_length(event);
+	if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
+		return length;
+	length -= RB_EVNT_HDR_SIZE;
+	if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
+                length -= sizeof(event->array[0]);
+	return length;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_event_length);
+
+/* inline for ring buffer fast paths */
+static __always_inline void *
+rb_event_data(struct ring_buffer_event *event)
+{
+	if (extended_time(event))
+		event = skip_time_extend(event);
+	WARN_ON_ONCE(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
+	/* If length is in len field, then array[0] has the data */
+	if (event->type_len)
+		return (void *)&event->array[0];
+	/* Otherwise length is in array[0] and array[1] has the data */
+	return (void *)&event->array[1];
+}
+
+/**
+ * ring_buffer_event_data - return the data of the event
+ * @event: the event to get the data from
+ */
+void *ring_buffer_event_data(struct ring_buffer_event *event)
+{
+	return rb_event_data(event);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_event_data);
+
+#define for_each_buffer_cpu(buffer, cpu)		\
+	for_each_cpu(cpu, buffer->cpumask)
+
+#define for_each_online_buffer_cpu(buffer, cpu)		\
+	for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
+
+#define TS_SHIFT	27
+#define TS_MASK		((1ULL << TS_SHIFT) - 1)
+#define TS_DELTA_TEST	(~TS_MASK)
+
+static u64 rb_event_time_stamp(struct ring_buffer_event *event)
+{
+	u64 ts;
+
+	ts = event->array[0];
+	ts <<= TS_SHIFT;
+	ts += event->time_delta;
+
+	return ts;
+}
+
+/* Flag when events were overwritten */
+#define RB_MISSED_EVENTS	(1 << 31)
+/* Missed count stored at end */
+#define RB_MISSED_STORED	(1 << 30)
+
+struct buffer_data_page {
+	u64		 time_stamp;	/* page time stamp */
+	local_t		 commit;	/* write committed index */
+	unsigned char	 data[] RB_ALIGN_DATA;	/* data of buffer page */
+};
+
+/*
+ * Note, the buffer_page list must be first. The buffer pages
+ * are allocated in cache lines, which means that each buffer
+ * page will be at the beginning of a cache line, and thus
+ * the least significant bits will be zero. We use this to
+ * add flags in the list struct pointers, to make the ring buffer
+ * lockless.
+ */
+struct buffer_page {
+	struct list_head list;		/* list of buffer pages */
+	local_t		 write;		/* index for next write */
+	unsigned	 read;		/* index for next read */
+	local_t		 entries;	/* entries on this page */
+	unsigned long	 real_end;	/* real end of data */
+	struct buffer_data_page *page;	/* Actual data page */
+};
+
+/*
+ * The buffer page counters, write and entries, must be reset
+ * atomically when crossing page boundaries. To synchronize this
+ * update, two counters are inserted into the number. One is
+ * the actual counter for the write position or count on the page.
+ *
+ * The other is a counter of updaters. Before an update happens
+ * the update partition of the counter is incremented. This will
+ * allow the updater to update the counter atomically.
+ *
+ * The counter is 20 bits, and the state data is 12.
+ */
+#define RB_WRITE_MASK		0xfffff
+#define RB_WRITE_INTCNT		(1 << 20)
+
+static void rb_init_page(struct buffer_data_page *bpage)
+{
+	local_set(&bpage->commit, 0);
+}
+
+static __always_inline unsigned int rb_page_commit(struct buffer_page *bpage)
+{
+	return local_read(&bpage->page->commit);
+}
+
+static void free_buffer_page(struct buffer_page *bpage)
+{
+	free_page((unsigned long)bpage->page);
+	kfree(bpage);
+}
+
+/*
+ * We need to fit the time_stamp delta into 27 bits.
+ */
+static inline bool test_time_stamp(u64 delta)
+{
+	return !!(delta & TS_DELTA_TEST);
+}
+
+#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
+
+/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
+#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
+
+int ring_buffer_print_page_header(struct trace_seq *s)
+{
+	struct buffer_data_page field;
+
+	trace_seq_printf(s, "\tfield: u64 timestamp;\t"
+			 "offset:0;\tsize:%u;\tsigned:%u;\n",
+			 (unsigned int)sizeof(field.time_stamp),
+			 (unsigned int)is_signed_type(u64));
+
+	trace_seq_printf(s, "\tfield: local_t commit;\t"
+			 "offset:%u;\tsize:%u;\tsigned:%u;\n",
+			 (unsigned int)offsetof(typeof(field), commit),
+			 (unsigned int)sizeof(field.commit),
+			 (unsigned int)is_signed_type(long));
+
+	trace_seq_printf(s, "\tfield: int overwrite;\t"
+			 "offset:%u;\tsize:%u;\tsigned:%u;\n",
+			 (unsigned int)offsetof(typeof(field), commit),
+			 1,
+			 (unsigned int)is_signed_type(long));
+
+	trace_seq_printf(s, "\tfield: char data;\t"
+			 "offset:%u;\tsize:%u;\tsigned:%u;\n",
+			 (unsigned int)offsetof(typeof(field), data),
+			 (unsigned int)BUF_PAGE_SIZE,
+			 (unsigned int)is_signed_type(char));
+
+	return !trace_seq_has_overflowed(s);
+}
+
+struct rb_irq_work {
+	struct irq_work			work;
+	wait_queue_head_t		waiters;
+	wait_queue_head_t		full_waiters;
+	long				wait_index;
+	bool				waiters_pending;
+	bool				full_waiters_pending;
+	bool				wakeup_full;
+};
+
+/*
+ * Structure to hold event state and handle nested events.
+ */
+struct rb_event_info {
+	u64			ts;
+	u64			delta;
+	u64			before;
+	u64			after;
+	unsigned long		length;
+	struct buffer_page	*tail_page;
+	int			add_timestamp;
+};
+
+/*
+ * Used for the add_timestamp
+ *  NONE
+ *  EXTEND - wants a time extend
+ *  ABSOLUTE - the buffer requests all events to have absolute time stamps
+ *  FORCE - force a full time stamp.
+ */
+enum {
+	RB_ADD_STAMP_NONE		= 0,
+	RB_ADD_STAMP_EXTEND		= BIT(1),
+	RB_ADD_STAMP_ABSOLUTE		= BIT(2),
+	RB_ADD_STAMP_FORCE		= BIT(3)
+};
+/*
+ * Used for which event context the event is in.
+ *  TRANSITION = 0
+ *  NMI     = 1
+ *  IRQ     = 2
+ *  SOFTIRQ = 3
+ *  NORMAL  = 4
+ *
+ * See trace_recursive_lock() comment below for more details.
+ */
+enum {
+	RB_CTX_TRANSITION,
+	RB_CTX_NMI,
+	RB_CTX_IRQ,
+	RB_CTX_SOFTIRQ,
+	RB_CTX_NORMAL,
+	RB_CTX_MAX
+};
+
+#if BITS_PER_LONG == 32
+#define RB_TIME_32
+#endif
+
+/* To test on 64 bit machines */
+//#define RB_TIME_32
+
+#ifdef RB_TIME_32
+
+struct rb_time_struct {
+	local_t		cnt;
+	local_t		top;
+	local_t		bottom;
+	local_t		msb;
+};
+#else
+#include <asm/local64.h>
+struct rb_time_struct {
+	local64_t	time;
+};
+#endif
+typedef struct rb_time_struct rb_time_t;
+
+#define MAX_NEST	5
+
+/*
+ * head_page == tail_page && head == tail then buffer is empty.
+ */
+struct ring_buffer_per_cpu {
+	int				cpu;
+	atomic_t			record_disabled;
+	atomic_t			resize_disabled;
+	struct trace_buffer	*buffer;
+	raw_spinlock_t			reader_lock;	/* serialize readers */
+	arch_spinlock_t			lock;
+	struct lock_class_key		lock_key;
+	struct buffer_data_page		*free_page;
+	unsigned long			nr_pages;
+	unsigned int			current_context;
+	struct list_head		*pages;
+	struct buffer_page		*head_page;	/* read from head */
+	struct buffer_page		*tail_page;	/* write to tail */
+	struct buffer_page		*commit_page;	/* committed pages */
+	struct buffer_page		*reader_page;
+	unsigned long			lost_events;
+	unsigned long			last_overrun;
+	unsigned long			nest;
+	local_t				entries_bytes;
+	local_t				entries;
+	local_t				overrun;
+	local_t				commit_overrun;
+	local_t				dropped_events;
+	local_t				committing;
+	local_t				commits;
+	local_t				pages_touched;
+	local_t				pages_lost;
+	local_t				pages_read;
+	long				last_pages_touch;
+	size_t				shortest_full;
+	unsigned long			read;
+	unsigned long			read_bytes;
+	rb_time_t			write_stamp;
+	rb_time_t			before_stamp;
+	u64				event_stamp[MAX_NEST];
+	u64				read_stamp;
+	/* pages removed since last reset */
+	unsigned long			pages_removed;
+	/* ring buffer pages to update, > 0 to add, < 0 to remove */
+	long				nr_pages_to_update;
+	struct list_head		new_pages; /* new pages to add */
+	struct work_struct		update_pages_work;
+	struct completion		update_done;
+
+	struct rb_irq_work		irq_work;
+};
+
+struct trace_buffer {
+	unsigned			flags;
+	int				cpus;
+	atomic_t			record_disabled;
+	atomic_t			resizing;
+	cpumask_var_t			cpumask;
+
+	struct lock_class_key		*reader_lock_key;
+
+	struct mutex			mutex;
+
+	struct ring_buffer_per_cpu	**buffers;
+
+	struct hlist_node		node;
+	u64				(*clock)(void);
+
+	struct rb_irq_work		irq_work;
+	bool				time_stamp_abs;
+};
+
+struct ring_buffer_iter {
+	struct ring_buffer_per_cpu	*cpu_buffer;
+	unsigned long			head;
+	unsigned long			next_event;
+	struct buffer_page		*head_page;
+	struct buffer_page		*cache_reader_page;
+	unsigned long			cache_read;
+	unsigned long			cache_pages_removed;
+	u64				read_stamp;
+	u64				page_stamp;
+	struct ring_buffer_event	*event;
+	int				missed_events;
+};
+
+#ifdef RB_TIME_32
+
+/*
+ * On 32 bit machines, local64_t is very expensive. As the ring
+ * buffer doesn't need all the features of a true 64 bit atomic,
+ * on 32 bit, it uses these functions (64 still uses local64_t).
+ *
+ * For the ring buffer, 64 bit required operations for the time is
+ * the following:
+ *
+ *  - Reads may fail if it interrupted a modification of the time stamp.
+ *      It will succeed if it did not interrupt another write even if
+ *      the read itself is interrupted by a write.
+ *      It returns whether it was successful or not.
+ *
+ *  - Writes always succeed and will overwrite other writes and writes
+ *      that were done by events interrupting the current write.
+ *
+ *  - A write followed by a read of the same time stamp will always succeed,
+ *      but may not contain the same value.
+ *
+ *  - A cmpxchg will fail if it interrupted another write or cmpxchg.
+ *      Other than that, it acts like a normal cmpxchg.
+ *
+ * The 60 bit time stamp is broken up by 30 bits in a top and bottom half
+ *  (bottom being the least significant 30 bits of the 60 bit time stamp).
+ *
+ * The two most significant bits of each half holds a 2 bit counter (0-3).
+ * Each update will increment this counter by one.
+ * When reading the top and bottom, if the two counter bits match then the
+ *  top and bottom together make a valid 60 bit number.
+ */
+#define RB_TIME_SHIFT	30
+#define RB_TIME_VAL_MASK ((1 << RB_TIME_SHIFT) - 1)
+#define RB_TIME_MSB_SHIFT	 60
+
+static inline int rb_time_cnt(unsigned long val)
+{
+	return (val >> RB_TIME_SHIFT) & 3;
+}
+
+static inline u64 rb_time_val(unsigned long top, unsigned long bottom)
+{
+	u64 val;
+
+	val = top & RB_TIME_VAL_MASK;
+	val <<= RB_TIME_SHIFT;
+	val |= bottom & RB_TIME_VAL_MASK;
+
+	return val;
+}
+
+static inline bool __rb_time_read(rb_time_t *t, u64 *ret, unsigned long *cnt)
+{
+	unsigned long top, bottom, msb;
+	unsigned long c;
+
+	/*
+	 * If the read is interrupted by a write, then the cnt will
+	 * be different. Loop until both top and bottom have been read
+	 * without interruption.
+	 */
+	do {
+		c = local_read(&t->cnt);
+		top = local_read(&t->top);
+		bottom = local_read(&t->bottom);
+		msb = local_read(&t->msb);
+	} while (c != local_read(&t->cnt));
+
+	*cnt = rb_time_cnt(top);
+
+	/* If top, msb or bottom counts don't match, this interrupted a write */
+	if (*cnt != rb_time_cnt(msb) || *cnt != rb_time_cnt(bottom))
+		return false;
+
+	/* The shift to msb will lose its cnt bits */
+	*ret = rb_time_val(top, bottom) | ((u64)msb << RB_TIME_MSB_SHIFT);
+	return true;
+}
+
+static bool rb_time_read(rb_time_t *t, u64 *ret)
+{
+	unsigned long cnt;
+
+	return __rb_time_read(t, ret, &cnt);
+}
+
+static inline unsigned long rb_time_val_cnt(unsigned long val, unsigned long cnt)
+{
+	return (val & RB_TIME_VAL_MASK) | ((cnt & 3) << RB_TIME_SHIFT);
+}
+
+static inline void rb_time_split(u64 val, unsigned long *top, unsigned long *bottom,
+				 unsigned long *msb)
+{
+	*top = (unsigned long)((val >> RB_TIME_SHIFT) & RB_TIME_VAL_MASK);
+	*bottom = (unsigned long)(val & RB_TIME_VAL_MASK);
+	*msb = (unsigned long)(val >> RB_TIME_MSB_SHIFT);
+}
+
+static inline void rb_time_val_set(local_t *t, unsigned long val, unsigned long cnt)
+{
+	val = rb_time_val_cnt(val, cnt);
+	local_set(t, val);
+}
+
+static void rb_time_set(rb_time_t *t, u64 val)
+{
+	unsigned long cnt, top, bottom, msb;
+
+	rb_time_split(val, &top, &bottom, &msb);
+
+	/* Writes always succeed with a valid number even if it gets interrupted. */
+	do {
+		cnt = local_inc_return(&t->cnt);
+		rb_time_val_set(&t->top, top, cnt);
+		rb_time_val_set(&t->bottom, bottom, cnt);
+		rb_time_val_set(&t->msb, val >> RB_TIME_MSB_SHIFT, cnt);
+	} while (cnt != local_read(&t->cnt));
+}
+
+static inline bool
+rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set)
+{
+	return local_try_cmpxchg(l, &expect, set);
+}
+
+#else /* 64 bits */
+
+/* local64_t always succeeds */
+
+static inline bool rb_time_read(rb_time_t *t, u64 *ret)
+{
+	*ret = local64_read(&t->time);
+	return true;
+}
+static void rb_time_set(rb_time_t *t, u64 val)
+{
+	local64_set(&t->time, val);
+}
+#endif
+
+/*
+ * Enable this to make sure that the event passed to
+ * ring_buffer_event_time_stamp() is not committed and also
+ * is on the buffer that it passed in.
+ */
+//#define RB_VERIFY_EVENT
+#ifdef RB_VERIFY_EVENT
+static struct list_head *rb_list_head(struct list_head *list);
+static void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
+			 void *event)
+{
+	struct buffer_page *page = cpu_buffer->commit_page;
+	struct buffer_page *tail_page = READ_ONCE(cpu_buffer->tail_page);
+	struct list_head *next;
+	long commit, write;
+	unsigned long addr = (unsigned long)event;
+	bool done = false;
+	int stop = 0;
+
+	/* Make sure the event exists and is not committed yet */
+	do {
+		if (page == tail_page || WARN_ON_ONCE(stop++ > 100))
+			done = true;
+		commit = local_read(&page->page->commit);
+		write = local_read(&page->write);
+		if (addr >= (unsigned long)&page->page->data[commit] &&
+		    addr < (unsigned long)&page->page->data[write])
+			return;
+
+		next = rb_list_head(page->list.next);
+		page = list_entry(next, struct buffer_page, list);
+	} while (!done);
+	WARN_ON_ONCE(1);
+}
+#else
+static inline void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
+			 void *event)
+{
+}
+#endif
+
+/*
+ * The absolute time stamp drops the 5 MSBs and some clocks may
+ * require them. The rb_fix_abs_ts() will take a previous full
+ * time stamp, and add the 5 MSB of that time stamp on to the
+ * saved absolute time stamp. Then they are compared in case of
+ * the unlikely event that the latest time stamp incremented
+ * the 5 MSB.
+ */
+static inline u64 rb_fix_abs_ts(u64 abs, u64 save_ts)
+{
+	if (save_ts & TS_MSB) {
+		abs |= save_ts & TS_MSB;
+		/* Check for overflow */
+		if (unlikely(abs < save_ts))
+			abs += 1ULL << 59;
+	}
+	return abs;
+}
+
+static inline u64 rb_time_stamp(struct trace_buffer *buffer);
+
+/**
+ * ring_buffer_event_time_stamp - return the event's current time stamp
+ * @buffer: The buffer that the event is on
+ * @event: the event to get the time stamp of
+ *
+ * Note, this must be called after @event is reserved, and before it is
+ * committed to the ring buffer. And must be called from the same
+ * context where the event was reserved (normal, softirq, irq, etc).
+ *
+ * Returns the time stamp associated with the current event.
+ * If the event has an extended time stamp, then that is used as
+ * the time stamp to return.
+ * In the highly unlikely case that the event was nested more than
+ * the max nesting, then the write_stamp of the buffer is returned,
+ * otherwise  current time is returned, but that really neither of
+ * the last two cases should ever happen.
+ */
+u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
+				 struct ring_buffer_event *event)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[smp_processor_id()];
+	unsigned int nest;
+	u64 ts;
+
+	/* If the event includes an absolute time, then just use that */
+	if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
+		ts = rb_event_time_stamp(event);
+		return rb_fix_abs_ts(ts, cpu_buffer->tail_page->page->time_stamp);
+	}
+
+	nest = local_read(&cpu_buffer->committing);
+	verify_event(cpu_buffer, event);
+	if (WARN_ON_ONCE(!nest))
+		goto fail;
+
+	/* Read the current saved nesting level time stamp */
+	if (likely(--nest < MAX_NEST))
+		return cpu_buffer->event_stamp[nest];
+
+	/* Shouldn't happen, warn if it does */
+	WARN_ONCE(1, "nest (%d) greater than max", nest);
+
+ fail:
+	/* Can only fail on 32 bit */
+	if (!rb_time_read(&cpu_buffer->write_stamp, &ts))
+		/* Screw it, just read the current time */
+		ts = rb_time_stamp(cpu_buffer->buffer);
+
+	return ts;
+}
+
+/**
+ * ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
+ * @buffer: The ring_buffer to get the number of pages from
+ * @cpu: The cpu of the ring_buffer to get the number of pages from
+ *
+ * Returns the number of pages used by a per_cpu buffer of the ring buffer.
+ */
+size_t ring_buffer_nr_pages(struct trace_buffer *buffer, int cpu)
+{
+	return buffer->buffers[cpu]->nr_pages;
+}
+
+/**
+ * ring_buffer_nr_dirty_pages - get the number of used pages in the ring buffer
+ * @buffer: The ring_buffer to get the number of pages from
+ * @cpu: The cpu of the ring_buffer to get the number of pages from
+ *
+ * Returns the number of pages that have content in the ring buffer.
+ */
+size_t ring_buffer_nr_dirty_pages(struct trace_buffer *buffer, int cpu)
+{
+	size_t read;
+	size_t lost;
+	size_t cnt;
+
+	read = local_read(&buffer->buffers[cpu]->pages_read);
+	lost = local_read(&buffer->buffers[cpu]->pages_lost);
+	cnt = local_read(&buffer->buffers[cpu]->pages_touched);
+
+	if (WARN_ON_ONCE(cnt < lost))
+		return 0;
+
+	cnt -= lost;
+
+	/* The reader can read an empty page, but not more than that */
+	if (cnt < read) {
+		WARN_ON_ONCE(read > cnt + 1);
+		return 0;
+	}
+
+	return cnt - read;
+}
+
+static __always_inline bool full_hit(struct trace_buffer *buffer, int cpu, int full)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+	size_t nr_pages;
+	size_t dirty;
+
+	nr_pages = cpu_buffer->nr_pages;
+	if (!nr_pages || !full)
+		return true;
+
+	/*
+	 * Add one as dirty will never equal nr_pages, as the sub-buffer
+	 * that the writer is on is not counted as dirty.
+	 * This is needed if "buffer_percent" is set to 100.
+	 */
+	dirty = ring_buffer_nr_dirty_pages(buffer, cpu) + 1;
+
+	return (dirty * 100) >= (full * nr_pages);
+}
+
+/*
+ * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
+ *
+ * Schedules a delayed work to wake up any task that is blocked on the
+ * ring buffer waiters queue.
+ */
+static void rb_wake_up_waiters(struct irq_work *work)
+{
+	struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
+
+	wake_up_all(&rbwork->waiters);
+	if (rbwork->full_waiters_pending || rbwork->wakeup_full) {
+		rbwork->wakeup_full = false;
+		rbwork->full_waiters_pending = false;
+		wake_up_all(&rbwork->full_waiters);
+	}
+}
+
+/**
+ * ring_buffer_wake_waiters - wake up any waiters on this ring buffer
+ * @buffer: The ring buffer to wake waiters on
+ * @cpu: The CPU buffer to wake waiters on
+ *
+ * In the case of a file that represents a ring buffer is closing,
+ * it is prudent to wake up any waiters that are on this.
+ */
+void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct rb_irq_work *rbwork;
+
+	if (!buffer)
+		return;
+
+	if (cpu == RING_BUFFER_ALL_CPUS) {
+
+		/* Wake up individual ones too. One level recursion */
+		for_each_buffer_cpu(buffer, cpu)
+			ring_buffer_wake_waiters(buffer, cpu);
+
+		rbwork = &buffer->irq_work;
+	} else {
+		if (WARN_ON_ONCE(!buffer->buffers))
+			return;
+		if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
+			return;
+
+		cpu_buffer = buffer->buffers[cpu];
+		/* The CPU buffer may not have been initialized yet */
+		if (!cpu_buffer)
+			return;
+		rbwork = &cpu_buffer->irq_work;
+	}
+
+	rbwork->wait_index++;
+	/* make sure the waiters see the new index */
+	smp_wmb();
+
+	/* This can be called in any context */
+	irq_work_queue(&rbwork->work);
+}
+
+/**
+ * ring_buffer_wait - wait for input to the ring buffer
+ * @buffer: buffer to wait on
+ * @cpu: the cpu buffer to wait on
+ * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
+ *
+ * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
+ * as data is added to any of the @buffer's cpu buffers. Otherwise
+ * it will wait for data to be added to a specific cpu buffer.
+ */
+int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	DEFINE_WAIT(wait);
+	struct rb_irq_work *work;
+	long wait_index;
+	int ret = 0;
+
+	/*
+	 * Depending on what the caller is waiting for, either any
+	 * data in any cpu buffer, or a specific buffer, put the
+	 * caller on the appropriate wait queue.
+	 */
+	if (cpu == RING_BUFFER_ALL_CPUS) {
+		work = &buffer->irq_work;
+		/* Full only makes sense on per cpu reads */
+		full = 0;
+	} else {
+		if (!cpumask_test_cpu(cpu, buffer->cpumask))
+			return -ENODEV;
+		cpu_buffer = buffer->buffers[cpu];
+		work = &cpu_buffer->irq_work;
+	}
+
+	wait_index = READ_ONCE(work->wait_index);
+
+	while (true) {
+		if (full)
+			prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
+		else
+			prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
+
+		/*
+		 * The events can happen in critical sections where
+		 * checking a work queue can cause deadlocks.
+		 * After adding a task to the queue, this flag is set
+		 * only to notify events to try to wake up the queue
+		 * using irq_work.
+		 *
+		 * We don't clear it even if the buffer is no longer
+		 * empty. The flag only causes the next event to run
+		 * irq_work to do the work queue wake up. The worse
+		 * that can happen if we race with !trace_empty() is that
+		 * an event will cause an irq_work to try to wake up
+		 * an empty queue.
+		 *
+		 * There's no reason to protect this flag either, as
+		 * the work queue and irq_work logic will do the necessary
+		 * synchronization for the wake ups. The only thing
+		 * that is necessary is that the wake up happens after
+		 * a task has been queued. It's OK for spurious wake ups.
+		 */
+		if (full)
+			work->full_waiters_pending = true;
+		else
+			work->waiters_pending = true;
+
+		if (signal_pending(current)) {
+			ret = -EINTR;
+			break;
+		}
+
+		if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
+			break;
+
+		if (cpu != RING_BUFFER_ALL_CPUS &&
+		    !ring_buffer_empty_cpu(buffer, cpu)) {
+			unsigned long flags;
+			bool pagebusy;
+			bool done;
+
+			if (!full)
+				break;
+
+			raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+			pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
+			done = !pagebusy && full_hit(buffer, cpu, full);
+
+			if (!cpu_buffer->shortest_full ||
+			    cpu_buffer->shortest_full > full)
+				cpu_buffer->shortest_full = full;
+			raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+			if (done)
+				break;
+		}
+
+		schedule();
+
+		/* Make sure to see the new wait index */
+		smp_rmb();
+		if (wait_index != work->wait_index)
+			break;
+	}
+
+	if (full)
+		finish_wait(&work->full_waiters, &wait);
+	else
+		finish_wait(&work->waiters, &wait);
+
+	return ret;
+}
+
+/**
+ * ring_buffer_poll_wait - poll on buffer input
+ * @buffer: buffer to wait on
+ * @cpu: the cpu buffer to wait on
+ * @filp: the file descriptor
+ * @poll_table: The poll descriptor
+ * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
+ *
+ * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
+ * as data is added to any of the @buffer's cpu buffers. Otherwise
+ * it will wait for data to be added to a specific cpu buffer.
+ *
+ * Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers,
+ * zero otherwise.
+ */
+__poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
+			  struct file *filp, poll_table *poll_table, int full)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct rb_irq_work *work;
+
+	if (cpu == RING_BUFFER_ALL_CPUS) {
+		work = &buffer->irq_work;
+		full = 0;
+	} else {
+		if (!cpumask_test_cpu(cpu, buffer->cpumask))
+			return -EINVAL;
+
+		cpu_buffer = buffer->buffers[cpu];
+		work = &cpu_buffer->irq_work;
+	}
+
+	if (full) {
+		poll_wait(filp, &work->full_waiters, poll_table);
+		work->full_waiters_pending = true;
+		if (!cpu_buffer->shortest_full ||
+		    cpu_buffer->shortest_full > full)
+			cpu_buffer->shortest_full = full;
+	} else {
+		poll_wait(filp, &work->waiters, poll_table);
+		work->waiters_pending = true;
+	}
+
+	/*
+	 * There's a tight race between setting the waiters_pending and
+	 * checking if the ring buffer is empty.  Once the waiters_pending bit
+	 * is set, the next event will wake the task up, but we can get stuck
+	 * if there's only a single event in.
+	 *
+	 * FIXME: Ideally, we need a memory barrier on the writer side as well,
+	 * but adding a memory barrier to all events will cause too much of a
+	 * performance hit in the fast path.  We only need a memory barrier when
+	 * the buffer goes from empty to having content.  But as this race is
+	 * extremely small, and it's not a problem if another event comes in, we
+	 * will fix it later.
+	 */
+	smp_mb();
+
+	if (full)
+		return full_hit(buffer, cpu, full) ? EPOLLIN | EPOLLRDNORM : 0;
+
+	if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
+	    (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
+		return EPOLLIN | EPOLLRDNORM;
+	return 0;
+}
+
+/* buffer may be either ring_buffer or ring_buffer_per_cpu */
+#define RB_WARN_ON(b, cond)						\
+	({								\
+		int _____ret = unlikely(cond);				\
+		if (_____ret) {						\
+			if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
+				struct ring_buffer_per_cpu *__b =	\
+					(void *)b;			\
+				atomic_inc(&__b->buffer->record_disabled); \
+			} else						\
+				atomic_inc(&b->record_disabled);	\
+			WARN_ON(1);					\
+		}							\
+		_____ret;						\
+	})
+
+/* Up this if you want to test the TIME_EXTENTS and normalization */
+#define DEBUG_SHIFT 0
+
+static inline u64 rb_time_stamp(struct trace_buffer *buffer)
+{
+	u64 ts;
+
+	/* Skip retpolines :-( */
+	if (IS_ENABLED(CONFIG_RETPOLINE) && likely(buffer->clock == trace_clock_local))
+		ts = trace_clock_local();
+	else
+		ts = buffer->clock();
+
+	/* shift to debug/test normalization and TIME_EXTENTS */
+	return ts << DEBUG_SHIFT;
+}
+
+u64 ring_buffer_time_stamp(struct trace_buffer *buffer)
+{
+	u64 time;
+
+	preempt_disable_notrace();
+	time = rb_time_stamp(buffer);
+	preempt_enable_notrace();
+
+	return time;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
+
+void ring_buffer_normalize_time_stamp(struct trace_buffer *buffer,
+				      int cpu, u64 *ts)
+{
+	/* Just stupid testing the normalize function and deltas */
+	*ts >>= DEBUG_SHIFT;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
+
+/*
+ * Making the ring buffer lockless makes things tricky.
+ * Although writes only happen on the CPU that they are on,
+ * and they only need to worry about interrupts. Reads can
+ * happen on any CPU.
+ *
+ * The reader page is always off the ring buffer, but when the
+ * reader finishes with a page, it needs to swap its page with
+ * a new one from the buffer. The reader needs to take from
+ * the head (writes go to the tail). But if a writer is in overwrite
+ * mode and wraps, it must push the head page forward.
+ *
+ * Here lies the problem.
+ *
+ * The reader must be careful to replace only the head page, and
+ * not another one. As described at the top of the file in the
+ * ASCII art, the reader sets its old page to point to the next
+ * page after head. It then sets the page after head to point to
+ * the old reader page. But if the writer moves the head page
+ * during this operation, the reader could end up with the tail.
+ *
+ * We use cmpxchg to help prevent this race. We also do something
+ * special with the page before head. We set the LSB to 1.
+ *
+ * When the writer must push the page forward, it will clear the
+ * bit that points to the head page, move the head, and then set
+ * the bit that points to the new head page.
+ *
+ * We also don't want an interrupt coming in and moving the head
+ * page on another writer. Thus we use the second LSB to catch
+ * that too. Thus:
+ *
+ * head->list->prev->next        bit 1          bit 0
+ *                              -------        -------
+ * Normal page                     0              0
+ * Points to head page             0              1
+ * New head page                   1              0
+ *
+ * Note we can not trust the prev pointer of the head page, because:
+ *
+ * +----+       +-----+        +-----+
+ * |    |------>|  T  |---X--->|  N  |
+ * |    |<------|     |        |     |
+ * +----+       +-----+        +-----+
+ *   ^                           ^ |
+ *   |          +-----+          | |
+ *   +----------|  R  |----------+ |
+ *              |     |<-----------+
+ *              +-----+
+ *
+ * Key:  ---X-->  HEAD flag set in pointer
+ *         T      Tail page
+ *         R      Reader page
+ *         N      Next page
+ *
+ * (see __rb_reserve_next() to see where this happens)
+ *
+ *  What the above shows is that the reader just swapped out
+ *  the reader page with a page in the buffer, but before it
+ *  could make the new header point back to the new page added
+ *  it was preempted by a writer. The writer moved forward onto
+ *  the new page added by the reader and is about to move forward
+ *  again.
+ *
+ *  You can see, it is legitimate for the previous pointer of
+ *  the head (or any page) not to point back to itself. But only
+ *  temporarily.
+ */
+
+#define RB_PAGE_NORMAL		0UL
+#define RB_PAGE_HEAD		1UL
+#define RB_PAGE_UPDATE		2UL
+
+
+#define RB_FLAG_MASK		3UL
+
+/* PAGE_MOVED is not part of the mask */
+#define RB_PAGE_MOVED		4UL
+
+/*
+ * rb_list_head - remove any bit
+ */
+static struct list_head *rb_list_head(struct list_head *list)
+{
+	unsigned long val = (unsigned long)list;
+
+	return (struct list_head *)(val & ~RB_FLAG_MASK);
+}
+
+/*
+ * rb_is_head_page - test if the given page is the head page
+ *
+ * Because the reader may move the head_page pointer, we can
+ * not trust what the head page is (it may be pointing to
+ * the reader page). But if the next page is a header page,
+ * its flags will be non zero.
+ */
+static inline int
+rb_is_head_page(struct buffer_page *page, struct list_head *list)
+{
+	unsigned long val;
+
+	val = (unsigned long)list->next;
+
+	if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
+		return RB_PAGE_MOVED;
+
+	return val & RB_FLAG_MASK;
+}
+
+/*
+ * rb_is_reader_page
+ *
+ * The unique thing about the reader page, is that, if the
+ * writer is ever on it, the previous pointer never points
+ * back to the reader page.
+ */
+static bool rb_is_reader_page(struct buffer_page *page)
+{
+	struct list_head *list = page->list.prev;
+
+	return rb_list_head(list->next) != &page->list;
+}
+
+/*
+ * rb_set_list_to_head - set a list_head to be pointing to head.
+ */
+static void rb_set_list_to_head(struct list_head *list)
+{
+	unsigned long *ptr;
+
+	ptr = (unsigned long *)&list->next;
+	*ptr |= RB_PAGE_HEAD;
+	*ptr &= ~RB_PAGE_UPDATE;
+}
+
+/*
+ * rb_head_page_activate - sets up head page
+ */
+static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct buffer_page *head;
+
+	head = cpu_buffer->head_page;
+	if (!head)
+		return;
+
+	/*
+	 * Set the previous list pointer to have the HEAD flag.
+	 */
+	rb_set_list_to_head(head->list.prev);
+}
+
+static void rb_list_head_clear(struct list_head *list)
+{
+	unsigned long *ptr = (unsigned long *)&list->next;
+
+	*ptr &= ~RB_FLAG_MASK;
+}
+
+/*
+ * rb_head_page_deactivate - clears head page ptr (for free list)
+ */
+static void
+rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct list_head *hd;
+
+	/* Go through the whole list and clear any pointers found. */
+	rb_list_head_clear(cpu_buffer->pages);
+
+	list_for_each(hd, cpu_buffer->pages)
+		rb_list_head_clear(hd);
+}
+
+static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
+			    struct buffer_page *head,
+			    struct buffer_page *prev,
+			    int old_flag, int new_flag)
+{
+	struct list_head *list;
+	unsigned long val = (unsigned long)&head->list;
+	unsigned long ret;
+
+	list = &prev->list;
+
+	val &= ~RB_FLAG_MASK;
+
+	ret = cmpxchg((unsigned long *)&list->next,
+		      val | old_flag, val | new_flag);
+
+	/* check if the reader took the page */
+	if ((ret & ~RB_FLAG_MASK) != val)
+		return RB_PAGE_MOVED;
+
+	return ret & RB_FLAG_MASK;
+}
+
+static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
+				   struct buffer_page *head,
+				   struct buffer_page *prev,
+				   int old_flag)
+{
+	return rb_head_page_set(cpu_buffer, head, prev,
+				old_flag, RB_PAGE_UPDATE);
+}
+
+static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
+				 struct buffer_page *head,
+				 struct buffer_page *prev,
+				 int old_flag)
+{
+	return rb_head_page_set(cpu_buffer, head, prev,
+				old_flag, RB_PAGE_HEAD);
+}
+
+static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
+				   struct buffer_page *head,
+				   struct buffer_page *prev,
+				   int old_flag)
+{
+	return rb_head_page_set(cpu_buffer, head, prev,
+				old_flag, RB_PAGE_NORMAL);
+}
+
+static inline void rb_inc_page(struct buffer_page **bpage)
+{
+	struct list_head *p = rb_list_head((*bpage)->list.next);
+
+	*bpage = list_entry(p, struct buffer_page, list);
+}
+
+static struct buffer_page *
+rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct buffer_page *head;
+	struct buffer_page *page;
+	struct list_head *list;
+	int i;
+
+	if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
+		return NULL;
+
+	/* sanity check */
+	list = cpu_buffer->pages;
+	if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
+		return NULL;
+
+	page = head = cpu_buffer->head_page;
+	/*
+	 * It is possible that the writer moves the header behind
+	 * where we started, and we miss in one loop.
+	 * A second loop should grab the header, but we'll do
+	 * three loops just because I'm paranoid.
+	 */
+	for (i = 0; i < 3; i++) {
+		do {
+			if (rb_is_head_page(page, page->list.prev)) {
+				cpu_buffer->head_page = page;
+				return page;
+			}
+			rb_inc_page(&page);
+		} while (page != head);
+	}
+
+	RB_WARN_ON(cpu_buffer, 1);
+
+	return NULL;
+}
+
+static bool rb_head_page_replace(struct buffer_page *old,
+				struct buffer_page *new)
+{
+	unsigned long *ptr = (unsigned long *)&old->list.prev->next;
+	unsigned long val;
+
+	val = *ptr & ~RB_FLAG_MASK;
+	val |= RB_PAGE_HEAD;
+
+	return try_cmpxchg(ptr, &val, (unsigned long)&new->list);
+}
+
+/*
+ * rb_tail_page_update - move the tail page forward
+ */
+static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
+			       struct buffer_page *tail_page,
+			       struct buffer_page *next_page)
+{
+	unsigned long old_entries;
+	unsigned long old_write;
+
+	/*
+	 * The tail page now needs to be moved forward.
+	 *
+	 * We need to reset the tail page, but without messing
+	 * with possible erasing of data brought in by interrupts
+	 * that have moved the tail page and are currently on it.
+	 *
+	 * We add a counter to the write field to denote this.
+	 */
+	old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
+	old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
+
+	local_inc(&cpu_buffer->pages_touched);
+	/*
+	 * Just make sure we have seen our old_write and synchronize
+	 * with any interrupts that come in.
+	 */
+	barrier();
+
+	/*
+	 * If the tail page is still the same as what we think
+	 * it is, then it is up to us to update the tail
+	 * pointer.
+	 */
+	if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
+		/* Zero the write counter */
+		unsigned long val = old_write & ~RB_WRITE_MASK;
+		unsigned long eval = old_entries & ~RB_WRITE_MASK;
+
+		/*
+		 * This will only succeed if an interrupt did
+		 * not come in and change it. In which case, we
+		 * do not want to modify it.
+		 *
+		 * We add (void) to let the compiler know that we do not care
+		 * about the return value of these functions. We use the
+		 * cmpxchg to only update if an interrupt did not already
+		 * do it for us. If the cmpxchg fails, we don't care.
+		 */
+		(void)local_cmpxchg(&next_page->write, old_write, val);
+		(void)local_cmpxchg(&next_page->entries, old_entries, eval);
+
+		/*
+		 * No need to worry about races with clearing out the commit.
+		 * it only can increment when a commit takes place. But that
+		 * only happens in the outer most nested commit.
+		 */
+		local_set(&next_page->page->commit, 0);
+
+		/* Again, either we update tail_page or an interrupt does */
+		(void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
+	}
+}
+
+static void rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
+			  struct buffer_page *bpage)
+{
+	unsigned long val = (unsigned long)bpage;
+
+	RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK);
+}
+
+/**
+ * rb_check_pages - integrity check of buffer pages
+ * @cpu_buffer: CPU buffer with pages to test
+ *
+ * As a safety measure we check to make sure the data pages have not
+ * been corrupted.
+ */
+static void rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct list_head *head = rb_list_head(cpu_buffer->pages);
+	struct list_head *tmp;
+
+	if (RB_WARN_ON(cpu_buffer,
+			rb_list_head(rb_list_head(head->next)->prev) != head))
+		return;
+
+	if (RB_WARN_ON(cpu_buffer,
+			rb_list_head(rb_list_head(head->prev)->next) != head))
+		return;
+
+	for (tmp = rb_list_head(head->next); tmp != head; tmp = rb_list_head(tmp->next)) {
+		if (RB_WARN_ON(cpu_buffer,
+				rb_list_head(rb_list_head(tmp->next)->prev) != tmp))
+			return;
+
+		if (RB_WARN_ON(cpu_buffer,
+				rb_list_head(rb_list_head(tmp->prev)->next) != tmp))
+			return;
+	}
+}
+
+static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
+		long nr_pages, struct list_head *pages)
+{
+	struct buffer_page *bpage, *tmp;
+	bool user_thread = current->mm != NULL;
+	gfp_t mflags;
+	long i;
+
+	/*
+	 * Check if the available memory is there first.
+	 * Note, si_mem_available() only gives us a rough estimate of available
+	 * memory. It may not be accurate. But we don't care, we just want
+	 * to prevent doing any allocation when it is obvious that it is
+	 * not going to succeed.
+	 */
+	i = si_mem_available();
+	if (i < nr_pages)
+		return -ENOMEM;
+
+	/*
+	 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
+	 * gracefully without invoking oom-killer and the system is not
+	 * destabilized.
+	 */
+	mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
+
+	/*
+	 * If a user thread allocates too much, and si_mem_available()
+	 * reports there's enough memory, even though there is not.
+	 * Make sure the OOM killer kills this thread. This can happen
+	 * even with RETRY_MAYFAIL because another task may be doing
+	 * an allocation after this task has taken all memory.
+	 * This is the task the OOM killer needs to take out during this
+	 * loop, even if it was triggered by an allocation somewhere else.
+	 */
+	if (user_thread)
+		set_current_oom_origin();
+	for (i = 0; i < nr_pages; i++) {
+		struct page *page;
+
+		bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
+				    mflags, cpu_to_node(cpu_buffer->cpu));
+		if (!bpage)
+			goto free_pages;
+
+		rb_check_bpage(cpu_buffer, bpage);
+
+		list_add(&bpage->list, pages);
+
+		page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu), mflags, 0);
+		if (!page)
+			goto free_pages;
+		bpage->page = page_address(page);
+		rb_init_page(bpage->page);
+
+		if (user_thread && fatal_signal_pending(current))
+			goto free_pages;
+	}
+	if (user_thread)
+		clear_current_oom_origin();
+
+	return 0;
+
+free_pages:
+	list_for_each_entry_safe(bpage, tmp, pages, list) {
+		list_del_init(&bpage->list);
+		free_buffer_page(bpage);
+	}
+	if (user_thread)
+		clear_current_oom_origin();
+
+	return -ENOMEM;
+}
+
+static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
+			     unsigned long nr_pages)
+{
+	LIST_HEAD(pages);
+
+	WARN_ON(!nr_pages);
+
+	if (__rb_allocate_pages(cpu_buffer, nr_pages, &pages))
+		return -ENOMEM;
+
+	/*
+	 * The ring buffer page list is a circular list that does not
+	 * start and end with a list head. All page list items point to
+	 * other pages.
+	 */
+	cpu_buffer->pages = pages.next;
+	list_del(&pages);
+
+	cpu_buffer->nr_pages = nr_pages;
+
+	rb_check_pages(cpu_buffer);
+
+	return 0;
+}
+
+static struct ring_buffer_per_cpu *
+rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct buffer_page *bpage;
+	struct page *page;
+	int ret;
+
+	cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
+				  GFP_KERNEL, cpu_to_node(cpu));
+	if (!cpu_buffer)
+		return NULL;
+
+	cpu_buffer->cpu = cpu;
+	cpu_buffer->buffer = buffer;
+	raw_spin_lock_init(&cpu_buffer->reader_lock);
+	lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
+	cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
+	INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
+	init_completion(&cpu_buffer->update_done);
+	init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
+	init_waitqueue_head(&cpu_buffer->irq_work.waiters);
+	init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
+
+	bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
+			    GFP_KERNEL, cpu_to_node(cpu));
+	if (!bpage)
+		goto fail_free_buffer;
+
+	rb_check_bpage(cpu_buffer, bpage);
+
+	cpu_buffer->reader_page = bpage;
+	page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
+	if (!page)
+		goto fail_free_reader;
+	bpage->page = page_address(page);
+	rb_init_page(bpage->page);
+
+	INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
+	INIT_LIST_HEAD(&cpu_buffer->new_pages);
+
+	ret = rb_allocate_pages(cpu_buffer, nr_pages);
+	if (ret < 0)
+		goto fail_free_reader;
+
+	cpu_buffer->head_page
+		= list_entry(cpu_buffer->pages, struct buffer_page, list);
+	cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
+
+	rb_head_page_activate(cpu_buffer);
+
+	return cpu_buffer;
+
+ fail_free_reader:
+	free_buffer_page(cpu_buffer->reader_page);
+
+ fail_free_buffer:
+	kfree(cpu_buffer);
+	return NULL;
+}
+
+static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct list_head *head = cpu_buffer->pages;
+	struct buffer_page *bpage, *tmp;
+
+	irq_work_sync(&cpu_buffer->irq_work.work);
+
+	free_buffer_page(cpu_buffer->reader_page);
+
+	if (head) {
+		rb_head_page_deactivate(cpu_buffer);
+
+		list_for_each_entry_safe(bpage, tmp, head, list) {
+			list_del_init(&bpage->list);
+			free_buffer_page(bpage);
+		}
+		bpage = list_entry(head, struct buffer_page, list);
+		free_buffer_page(bpage);
+	}
+
+	free_page((unsigned long)cpu_buffer->free_page);
+
+	kfree(cpu_buffer);
+}
+
+/**
+ * __ring_buffer_alloc - allocate a new ring_buffer
+ * @size: the size in bytes per cpu that is needed.
+ * @flags: attributes to set for the ring buffer.
+ * @key: ring buffer reader_lock_key.
+ *
+ * Currently the only flag that is available is the RB_FL_OVERWRITE
+ * flag. This flag means that the buffer will overwrite old data
+ * when the buffer wraps. If this flag is not set, the buffer will
+ * drop data when the tail hits the head.
+ */
+struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
+					struct lock_class_key *key)
+{
+	struct trace_buffer *buffer;
+	long nr_pages;
+	int bsize;
+	int cpu;
+	int ret;
+
+	/* keep it in its own cache line */
+	buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
+			 GFP_KERNEL);
+	if (!buffer)
+		return NULL;
+
+	if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
+		goto fail_free_buffer;
+
+	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
+	buffer->flags = flags;
+	buffer->clock = trace_clock_local;
+	buffer->reader_lock_key = key;
+
+	init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
+	init_waitqueue_head(&buffer->irq_work.waiters);
+
+	/* need at least two pages */
+	if (nr_pages < 2)
+		nr_pages = 2;
+
+	buffer->cpus = nr_cpu_ids;
+
+	bsize = sizeof(void *) * nr_cpu_ids;
+	buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
+				  GFP_KERNEL);
+	if (!buffer->buffers)
+		goto fail_free_cpumask;
+
+	cpu = raw_smp_processor_id();
+	cpumask_set_cpu(cpu, buffer->cpumask);
+	buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
+	if (!buffer->buffers[cpu])
+		goto fail_free_buffers;
+
+	ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
+	if (ret < 0)
+		goto fail_free_buffers;
+
+	mutex_init(&buffer->mutex);
+
+	return buffer;
+
+ fail_free_buffers:
+	for_each_buffer_cpu(buffer, cpu) {
+		if (buffer->buffers[cpu])
+			rb_free_cpu_buffer(buffer->buffers[cpu]);
+	}
+	kfree(buffer->buffers);
+
+ fail_free_cpumask:
+	free_cpumask_var(buffer->cpumask);
+
+ fail_free_buffer:
+	kfree(buffer);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
+
+/**
+ * ring_buffer_free - free a ring buffer.
+ * @buffer: the buffer to free.
+ */
+void
+ring_buffer_free(struct trace_buffer *buffer)
+{
+	int cpu;
+
+	cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
+
+	irq_work_sync(&buffer->irq_work.work);
+
+	for_each_buffer_cpu(buffer, cpu)
+		rb_free_cpu_buffer(buffer->buffers[cpu]);
+
+	kfree(buffer->buffers);
+	free_cpumask_var(buffer->cpumask);
+
+	kfree(buffer);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_free);
+
+void ring_buffer_set_clock(struct trace_buffer *buffer,
+			   u64 (*clock)(void))
+{
+	buffer->clock = clock;
+}
+
+void ring_buffer_set_time_stamp_abs(struct trace_buffer *buffer, bool abs)
+{
+	buffer->time_stamp_abs = abs;
+}
+
+bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
+{
+	return buffer->time_stamp_abs;
+}
+
+static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
+
+static inline unsigned long rb_page_entries(struct buffer_page *bpage)
+{
+	return local_read(&bpage->entries) & RB_WRITE_MASK;
+}
+
+static inline unsigned long rb_page_write(struct buffer_page *bpage)
+{
+	return local_read(&bpage->write) & RB_WRITE_MASK;
+}
+
+static bool
+rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
+{
+	struct list_head *tail_page, *to_remove, *next_page;
+	struct buffer_page *to_remove_page, *tmp_iter_page;
+	struct buffer_page *last_page, *first_page;
+	unsigned long nr_removed;
+	unsigned long head_bit;
+	int page_entries;
+
+	head_bit = 0;
+
+	raw_spin_lock_irq(&cpu_buffer->reader_lock);
+	atomic_inc(&cpu_buffer->record_disabled);
+	/*
+	 * We don't race with the readers since we have acquired the reader
+	 * lock. We also don't race with writers after disabling recording.
+	 * This makes it easy to figure out the first and the last page to be
+	 * removed from the list. We unlink all the pages in between including
+	 * the first and last pages. This is done in a busy loop so that we
+	 * lose the least number of traces.
+	 * The pages are freed after we restart recording and unlock readers.
+	 */
+	tail_page = &cpu_buffer->tail_page->list;
+
+	/*
+	 * tail page might be on reader page, we remove the next page
+	 * from the ring buffer
+	 */
+	if (cpu_buffer->tail_page == cpu_buffer->reader_page)
+		tail_page = rb_list_head(tail_page->next);
+	to_remove = tail_page;
+
+	/* start of pages to remove */
+	first_page = list_entry(rb_list_head(to_remove->next),
+				struct buffer_page, list);
+
+	for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
+		to_remove = rb_list_head(to_remove)->next;
+		head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
+	}
+	/* Read iterators need to reset themselves when some pages removed */
+	cpu_buffer->pages_removed += nr_removed;
+
+	next_page = rb_list_head(to_remove)->next;
+
+	/*
+	 * Now we remove all pages between tail_page and next_page.
+	 * Make sure that we have head_bit value preserved for the
+	 * next page
+	 */
+	tail_page->next = (struct list_head *)((unsigned long)next_page |
+						head_bit);
+	next_page = rb_list_head(next_page);
+	next_page->prev = tail_page;
+
+	/* make sure pages points to a valid page in the ring buffer */
+	cpu_buffer->pages = next_page;
+
+	/* update head page */
+	if (head_bit)
+		cpu_buffer->head_page = list_entry(next_page,
+						struct buffer_page, list);
+
+	/* pages are removed, resume tracing and then free the pages */
+	atomic_dec(&cpu_buffer->record_disabled);
+	raw_spin_unlock_irq(&cpu_buffer->reader_lock);
+
+	RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
+
+	/* last buffer page to remove */
+	last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
+				list);
+	tmp_iter_page = first_page;
+
+	do {
+		cond_resched();
+
+		to_remove_page = tmp_iter_page;
+		rb_inc_page(&tmp_iter_page);
+
+		/* update the counters */
+		page_entries = rb_page_entries(to_remove_page);
+		if (page_entries) {
+			/*
+			 * If something was added to this page, it was full
+			 * since it is not the tail page. So we deduct the
+			 * bytes consumed in ring buffer from here.
+			 * Increment overrun to account for the lost events.
+			 */
+			local_add(page_entries, &cpu_buffer->overrun);
+			local_sub(rb_page_commit(to_remove_page), &cpu_buffer->entries_bytes);
+			local_inc(&cpu_buffer->pages_lost);
+		}
+
+		/*
+		 * We have already removed references to this list item, just
+		 * free up the buffer_page and its page
+		 */
+		free_buffer_page(to_remove_page);
+		nr_removed--;
+
+	} while (to_remove_page != last_page);
+
+	RB_WARN_ON(cpu_buffer, nr_removed);
+
+	return nr_removed == 0;
+}
+
+static bool
+rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct list_head *pages = &cpu_buffer->new_pages;
+	unsigned long flags;
+	bool success;
+	int retries;
+
+	/* Can be called at early boot up, where interrupts must not been enabled */
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	/*
+	 * We are holding the reader lock, so the reader page won't be swapped
+	 * in the ring buffer. Now we are racing with the writer trying to
+	 * move head page and the tail page.
+	 * We are going to adapt the reader page update process where:
+	 * 1. We first splice the start and end of list of new pages between
+	 *    the head page and its previous page.
+	 * 2. We cmpxchg the prev_page->next to point from head page to the
+	 *    start of new pages list.
+	 * 3. Finally, we update the head->prev to the end of new list.
+	 *
+	 * We will try this process 10 times, to make sure that we don't keep
+	 * spinning.
+	 */
+	retries = 10;
+	success = false;
+	while (retries--) {
+		struct list_head *head_page, *prev_page, *r;
+		struct list_head *last_page, *first_page;
+		struct list_head *head_page_with_bit;
+		struct buffer_page *hpage = rb_set_head_page(cpu_buffer);
+
+		if (!hpage)
+			break;
+		head_page = &hpage->list;
+		prev_page = head_page->prev;
+
+		first_page = pages->next;
+		last_page  = pages->prev;
+
+		head_page_with_bit = (struct list_head *)
+				     ((unsigned long)head_page | RB_PAGE_HEAD);
+
+		last_page->next = head_page_with_bit;
+		first_page->prev = prev_page;
+
+		r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
+
+		if (r == head_page_with_bit) {
+			/*
+			 * yay, we replaced the page pointer to our new list,
+			 * now, we just have to update to head page's prev
+			 * pointer to point to end of list
+			 */
+			head_page->prev = last_page;
+			success = true;
+			break;
+		}
+	}
+
+	if (success)
+		INIT_LIST_HEAD(pages);
+	/*
+	 * If we weren't successful in adding in new pages, warn and stop
+	 * tracing
+	 */
+	RB_WARN_ON(cpu_buffer, !success);
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+	/* free pages if they weren't inserted */
+	if (!success) {
+		struct buffer_page *bpage, *tmp;
+		list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
+					 list) {
+			list_del_init(&bpage->list);
+			free_buffer_page(bpage);
+		}
+	}
+	return success;
+}
+
+static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	bool success;
+
+	if (cpu_buffer->nr_pages_to_update > 0)
+		success = rb_insert_pages(cpu_buffer);
+	else
+		success = rb_remove_pages(cpu_buffer,
+					-cpu_buffer->nr_pages_to_update);
+
+	if (success)
+		cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
+}
+
+static void update_pages_handler(struct work_struct *work)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
+			struct ring_buffer_per_cpu, update_pages_work);
+	rb_update_pages(cpu_buffer);
+	complete(&cpu_buffer->update_done);
+}
+
+/**
+ * ring_buffer_resize - resize the ring buffer
+ * @buffer: the buffer to resize.
+ * @size: the new size.
+ * @cpu_id: the cpu buffer to resize
+ *
+ * Minimum size is 2 * BUF_PAGE_SIZE.
+ *
+ * Returns 0 on success and < 0 on failure.
+ */
+int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
+			int cpu_id)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long nr_pages;
+	int cpu, err;
+
+	/*
+	 * Always succeed at resizing a non-existent buffer:
+	 */
+	if (!buffer)
+		return 0;
+
+	/* Make sure the requested buffer exists */
+	if (cpu_id != RING_BUFFER_ALL_CPUS &&
+	    !cpumask_test_cpu(cpu_id, buffer->cpumask))
+		return 0;
+
+	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
+
+	/* we need a minimum of two pages */
+	if (nr_pages < 2)
+		nr_pages = 2;
+
+	/* prevent another thread from changing buffer sizes */
+	mutex_lock(&buffer->mutex);
+	atomic_inc(&buffer->resizing);
+
+	if (cpu_id == RING_BUFFER_ALL_CPUS) {
+		/*
+		 * Don't succeed if resizing is disabled, as a reader might be
+		 * manipulating the ring buffer and is expecting a sane state while
+		 * this is true.
+		 */
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+			if (atomic_read(&cpu_buffer->resize_disabled)) {
+				err = -EBUSY;
+				goto out_err_unlock;
+			}
+		}
+
+		/* calculate the pages to update */
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+
+			cpu_buffer->nr_pages_to_update = nr_pages -
+							cpu_buffer->nr_pages;
+			/*
+			 * nothing more to do for removing pages or no update
+			 */
+			if (cpu_buffer->nr_pages_to_update <= 0)
+				continue;
+			/*
+			 * to add pages, make sure all new pages can be
+			 * allocated without receiving ENOMEM
+			 */
+			INIT_LIST_HEAD(&cpu_buffer->new_pages);
+			if (__rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
+						&cpu_buffer->new_pages)) {
+				/* not enough memory for new pages */
+				err = -ENOMEM;
+				goto out_err;
+			}
+
+			cond_resched();
+		}
+
+		cpus_read_lock();
+		/*
+		 * Fire off all the required work handlers
+		 * We can't schedule on offline CPUs, but it's not necessary
+		 * since we can change their buffer sizes without any race.
+		 */
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+			if (!cpu_buffer->nr_pages_to_update)
+				continue;
+
+			/* Can't run something on an offline CPU. */
+			if (!cpu_online(cpu)) {
+				rb_update_pages(cpu_buffer);
+				cpu_buffer->nr_pages_to_update = 0;
+			} else {
+				/* Run directly if possible. */
+				migrate_disable();
+				if (cpu != smp_processor_id()) {
+					migrate_enable();
+					schedule_work_on(cpu,
+							 &cpu_buffer->update_pages_work);
+				} else {
+					update_pages_handler(&cpu_buffer->update_pages_work);
+					migrate_enable();
+				}
+			}
+		}
+
+		/* wait for all the updates to complete */
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+			if (!cpu_buffer->nr_pages_to_update)
+				continue;
+
+			if (cpu_online(cpu))
+				wait_for_completion(&cpu_buffer->update_done);
+			cpu_buffer->nr_pages_to_update = 0;
+		}
+
+		cpus_read_unlock();
+	} else {
+		cpu_buffer = buffer->buffers[cpu_id];
+
+		if (nr_pages == cpu_buffer->nr_pages)
+			goto out;
+
+		/*
+		 * Don't succeed if resizing is disabled, as a reader might be
+		 * manipulating the ring buffer and is expecting a sane state while
+		 * this is true.
+		 */
+		if (atomic_read(&cpu_buffer->resize_disabled)) {
+			err = -EBUSY;
+			goto out_err_unlock;
+		}
+
+		cpu_buffer->nr_pages_to_update = nr_pages -
+						cpu_buffer->nr_pages;
+
+		INIT_LIST_HEAD(&cpu_buffer->new_pages);
+		if (cpu_buffer->nr_pages_to_update > 0 &&
+			__rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
+					    &cpu_buffer->new_pages)) {
+			err = -ENOMEM;
+			goto out_err;
+		}
+
+		cpus_read_lock();
+
+		/* Can't run something on an offline CPU. */
+		if (!cpu_online(cpu_id))
+			rb_update_pages(cpu_buffer);
+		else {
+			/* Run directly if possible. */
+			migrate_disable();
+			if (cpu_id == smp_processor_id()) {
+				rb_update_pages(cpu_buffer);
+				migrate_enable();
+			} else {
+				migrate_enable();
+				schedule_work_on(cpu_id,
+						 &cpu_buffer->update_pages_work);
+				wait_for_completion(&cpu_buffer->update_done);
+			}
+		}
+
+		cpu_buffer->nr_pages_to_update = 0;
+		cpus_read_unlock();
+	}
+
+ out:
+	/*
+	 * The ring buffer resize can happen with the ring buffer
+	 * enabled, so that the update disturbs the tracing as little
+	 * as possible. But if the buffer is disabled, we do not need
+	 * to worry about that, and we can take the time to verify
+	 * that the buffer is not corrupt.
+	 */
+	if (atomic_read(&buffer->record_disabled)) {
+		atomic_inc(&buffer->record_disabled);
+		/*
+		 * Even though the buffer was disabled, we must make sure
+		 * that it is truly disabled before calling rb_check_pages.
+		 * There could have been a race between checking
+		 * record_disable and incrementing it.
+		 */
+		synchronize_rcu();
+		for_each_buffer_cpu(buffer, cpu) {
+			cpu_buffer = buffer->buffers[cpu];
+			rb_check_pages(cpu_buffer);
+		}
+		atomic_dec(&buffer->record_disabled);
+	}
+
+	atomic_dec(&buffer->resizing);
+	mutex_unlock(&buffer->mutex);
+	return 0;
+
+ out_err:
+	for_each_buffer_cpu(buffer, cpu) {
+		struct buffer_page *bpage, *tmp;
+
+		cpu_buffer = buffer->buffers[cpu];
+		cpu_buffer->nr_pages_to_update = 0;
+
+		if (list_empty(&cpu_buffer->new_pages))
+			continue;
+
+		list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
+					list) {
+			list_del_init(&bpage->list);
+			free_buffer_page(bpage);
+		}
+	}
+ out_err_unlock:
+	atomic_dec(&buffer->resizing);
+	mutex_unlock(&buffer->mutex);
+	return err;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_resize);
+
+void ring_buffer_change_overwrite(struct trace_buffer *buffer, int val)
+{
+	mutex_lock(&buffer->mutex);
+	if (val)
+		buffer->flags |= RB_FL_OVERWRITE;
+	else
+		buffer->flags &= ~RB_FL_OVERWRITE;
+	mutex_unlock(&buffer->mutex);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
+
+static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
+{
+	return bpage->page->data + index;
+}
+
+static __always_inline struct ring_buffer_event *
+rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	return __rb_page_index(cpu_buffer->reader_page,
+			       cpu_buffer->reader_page->read);
+}
+
+static struct ring_buffer_event *
+rb_iter_head_event(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_event *event;
+	struct buffer_page *iter_head_page = iter->head_page;
+	unsigned long commit;
+	unsigned length;
+
+	if (iter->head != iter->next_event)
+		return iter->event;
+
+	/*
+	 * When the writer goes across pages, it issues a cmpxchg which
+	 * is a mb(), which will synchronize with the rmb here.
+	 * (see rb_tail_page_update() and __rb_reserve_next())
+	 */
+	commit = rb_page_commit(iter_head_page);
+	smp_rmb();
+
+	/* An event needs to be at least 8 bytes in size */
+	if (iter->head > commit - 8)
+		goto reset;
+
+	event = __rb_page_index(iter_head_page, iter->head);
+	length = rb_event_length(event);
+
+	/*
+	 * READ_ONCE() doesn't work on functions and we don't want the
+	 * compiler doing any crazy optimizations with length.
+	 */
+	barrier();
+
+	if ((iter->head + length) > commit || length > BUF_PAGE_SIZE)
+		/* Writer corrupted the read? */
+		goto reset;
+
+	memcpy(iter->event, event, length);
+	/*
+	 * If the page stamp is still the same after this rmb() then the
+	 * event was safely copied without the writer entering the page.
+	 */
+	smp_rmb();
+
+	/* Make sure the page didn't change since we read this */
+	if (iter->page_stamp != iter_head_page->page->time_stamp ||
+	    commit > rb_page_commit(iter_head_page))
+		goto reset;
+
+	iter->next_event = iter->head + length;
+	return iter->event;
+ reset:
+	/* Reset to the beginning */
+	iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
+	iter->head = 0;
+	iter->next_event = 0;
+	iter->missed_events = 1;
+	return NULL;
+}
+
+/* Size is determined by what has been committed */
+static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
+{
+	return rb_page_commit(bpage);
+}
+
+static __always_inline unsigned
+rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	return rb_page_commit(cpu_buffer->commit_page);
+}
+
+static __always_inline unsigned
+rb_event_index(struct ring_buffer_event *event)
+{
+	unsigned long addr = (unsigned long)event;
+
+	return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
+}
+
+static void rb_inc_iter(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+
+	/*
+	 * The iterator could be on the reader page (it starts there).
+	 * But the head could have moved, since the reader was
+	 * found. Check for this case and assign the iterator
+	 * to the head page instead of next.
+	 */
+	if (iter->head_page == cpu_buffer->reader_page)
+		iter->head_page = rb_set_head_page(cpu_buffer);
+	else
+		rb_inc_page(&iter->head_page);
+
+	iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
+	iter->head = 0;
+	iter->next_event = 0;
+}
+
+/*
+ * rb_handle_head_page - writer hit the head page
+ *
+ * Returns: +1 to retry page
+ *           0 to continue
+ *          -1 on error
+ */
+static int
+rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
+		    struct buffer_page *tail_page,
+		    struct buffer_page *next_page)
+{
+	struct buffer_page *new_head;
+	int entries;
+	int type;
+	int ret;
+
+	entries = rb_page_entries(next_page);
+
+	/*
+	 * The hard part is here. We need to move the head
+	 * forward, and protect against both readers on
+	 * other CPUs and writers coming in via interrupts.
+	 */
+	type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
+				       RB_PAGE_HEAD);
+
+	/*
+	 * type can be one of four:
+	 *  NORMAL - an interrupt already moved it for us
+	 *  HEAD   - we are the first to get here.
+	 *  UPDATE - we are the interrupt interrupting
+	 *           a current move.
+	 *  MOVED  - a reader on another CPU moved the next
+	 *           pointer to its reader page. Give up
+	 *           and try again.
+	 */
+
+	switch (type) {
+	case RB_PAGE_HEAD:
+		/*
+		 * We changed the head to UPDATE, thus
+		 * it is our responsibility to update
+		 * the counters.
+		 */
+		local_add(entries, &cpu_buffer->overrun);
+		local_sub(rb_page_commit(next_page), &cpu_buffer->entries_bytes);
+		local_inc(&cpu_buffer->pages_lost);
+
+		/*
+		 * The entries will be zeroed out when we move the
+		 * tail page.
+		 */
+
+		/* still more to do */
+		break;
+
+	case RB_PAGE_UPDATE:
+		/*
+		 * This is an interrupt that interrupt the
+		 * previous update. Still more to do.
+		 */
+		break;
+	case RB_PAGE_NORMAL:
+		/*
+		 * An interrupt came in before the update
+		 * and processed this for us.
+		 * Nothing left to do.
+		 */
+		return 1;
+	case RB_PAGE_MOVED:
+		/*
+		 * The reader is on another CPU and just did
+		 * a swap with our next_page.
+		 * Try again.
+		 */
+		return 1;
+	default:
+		RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
+		return -1;
+	}
+
+	/*
+	 * Now that we are here, the old head pointer is
+	 * set to UPDATE. This will keep the reader from
+	 * swapping the head page with the reader page.
+	 * The reader (on another CPU) will spin till
+	 * we are finished.
+	 *
+	 * We just need to protect against interrupts
+	 * doing the job. We will set the next pointer
+	 * to HEAD. After that, we set the old pointer
+	 * to NORMAL, but only if it was HEAD before.
+	 * otherwise we are an interrupt, and only
+	 * want the outer most commit to reset it.
+	 */
+	new_head = next_page;
+	rb_inc_page(&new_head);
+
+	ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
+				    RB_PAGE_NORMAL);
+
+	/*
+	 * Valid returns are:
+	 *  HEAD   - an interrupt came in and already set it.
+	 *  NORMAL - One of two things:
+	 *            1) We really set it.
+	 *            2) A bunch of interrupts came in and moved
+	 *               the page forward again.
+	 */
+	switch (ret) {
+	case RB_PAGE_HEAD:
+	case RB_PAGE_NORMAL:
+		/* OK */
+		break;
+	default:
+		RB_WARN_ON(cpu_buffer, 1);
+		return -1;
+	}
+
+	/*
+	 * It is possible that an interrupt came in,
+	 * set the head up, then more interrupts came in
+	 * and moved it again. When we get back here,
+	 * the page would have been set to NORMAL but we
+	 * just set it back to HEAD.
+	 *
+	 * How do you detect this? Well, if that happened
+	 * the tail page would have moved.
+	 */
+	if (ret == RB_PAGE_NORMAL) {
+		struct buffer_page *buffer_tail_page;
+
+		buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
+		/*
+		 * If the tail had moved passed next, then we need
+		 * to reset the pointer.
+		 */
+		if (buffer_tail_page != tail_page &&
+		    buffer_tail_page != next_page)
+			rb_head_page_set_normal(cpu_buffer, new_head,
+						next_page,
+						RB_PAGE_HEAD);
+	}
+
+	/*
+	 * If this was the outer most commit (the one that
+	 * changed the original pointer from HEAD to UPDATE),
+	 * then it is up to us to reset it to NORMAL.
+	 */
+	if (type == RB_PAGE_HEAD) {
+		ret = rb_head_page_set_normal(cpu_buffer, next_page,
+					      tail_page,
+					      RB_PAGE_UPDATE);
+		if (RB_WARN_ON(cpu_buffer,
+			       ret != RB_PAGE_UPDATE))
+			return -1;
+	}
+
+	return 0;
+}
+
+static inline void
+rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
+	      unsigned long tail, struct rb_event_info *info)
+{
+	struct buffer_page *tail_page = info->tail_page;
+	struct ring_buffer_event *event;
+	unsigned long length = info->length;
+
+	/*
+	 * Only the event that crossed the page boundary
+	 * must fill the old tail_page with padding.
+	 */
+	if (tail >= BUF_PAGE_SIZE) {
+		/*
+		 * If the page was filled, then we still need
+		 * to update the real_end. Reset it to zero
+		 * and the reader will ignore it.
+		 */
+		if (tail == BUF_PAGE_SIZE)
+			tail_page->real_end = 0;
+
+		local_sub(length, &tail_page->write);
+		return;
+	}
+
+	event = __rb_page_index(tail_page, tail);
+
+	/*
+	 * Save the original length to the meta data.
+	 * This will be used by the reader to add lost event
+	 * counter.
+	 */
+	tail_page->real_end = tail;
+
+	/*
+	 * If this event is bigger than the minimum size, then
+	 * we need to be careful that we don't subtract the
+	 * write counter enough to allow another writer to slip
+	 * in on this page.
+	 * We put in a discarded commit instead, to make sure
+	 * that this space is not used again, and this space will
+	 * not be accounted into 'entries_bytes'.
+	 *
+	 * If we are less than the minimum size, we don't need to
+	 * worry about it.
+	 */
+	if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
+		/* No room for any events */
+
+		/* Mark the rest of the page with padding */
+		rb_event_set_padding(event);
+
+		/* Make sure the padding is visible before the write update */
+		smp_wmb();
+
+		/* Set the write back to the previous setting */
+		local_sub(length, &tail_page->write);
+		return;
+	}
+
+	/* Put in a discarded event */
+	event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
+	event->type_len = RINGBUF_TYPE_PADDING;
+	/* time delta must be non zero */
+	event->time_delta = 1;
+
+	/* account for padding bytes */
+	local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
+
+	/* Make sure the padding is visible before the tail_page->write update */
+	smp_wmb();
+
+	/* Set write to end of buffer */
+	length = (tail + length) - BUF_PAGE_SIZE;
+	local_sub(length, &tail_page->write);
+}
+
+static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
+
+/*
+ * This is the slow path, force gcc not to inline it.
+ */
+static noinline struct ring_buffer_event *
+rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
+	     unsigned long tail, struct rb_event_info *info)
+{
+	struct buffer_page *tail_page = info->tail_page;
+	struct buffer_page *commit_page = cpu_buffer->commit_page;
+	struct trace_buffer *buffer = cpu_buffer->buffer;
+	struct buffer_page *next_page;
+	int ret;
+
+	next_page = tail_page;
+
+	rb_inc_page(&next_page);
+
+	/*
+	 * If for some reason, we had an interrupt storm that made
+	 * it all the way around the buffer, bail, and warn
+	 * about it.
+	 */
+	if (unlikely(next_page == commit_page)) {
+		local_inc(&cpu_buffer->commit_overrun);
+		goto out_reset;
+	}
+
+	/*
+	 * This is where the fun begins!
+	 *
+	 * We are fighting against races between a reader that
+	 * could be on another CPU trying to swap its reader
+	 * page with the buffer head.
+	 *
+	 * We are also fighting against interrupts coming in and
+	 * moving the head or tail on us as well.
+	 *
+	 * If the next page is the head page then we have filled
+	 * the buffer, unless the commit page is still on the
+	 * reader page.
+	 */
+	if (rb_is_head_page(next_page, &tail_page->list)) {
+
+		/*
+		 * If the commit is not on the reader page, then
+		 * move the header page.
+		 */
+		if (!rb_is_reader_page(cpu_buffer->commit_page)) {
+			/*
+			 * If we are not in overwrite mode,
+			 * this is easy, just stop here.
+			 */
+			if (!(buffer->flags & RB_FL_OVERWRITE)) {
+				local_inc(&cpu_buffer->dropped_events);
+				goto out_reset;
+			}
+
+			ret = rb_handle_head_page(cpu_buffer,
+						  tail_page,
+						  next_page);
+			if (ret < 0)
+				goto out_reset;
+			if (ret)
+				goto out_again;
+		} else {
+			/*
+			 * We need to be careful here too. The
+			 * commit page could still be on the reader
+			 * page. We could have a small buffer, and
+			 * have filled up the buffer with events
+			 * from interrupts and such, and wrapped.
+			 *
+			 * Note, if the tail page is also on the
+			 * reader_page, we let it move out.
+			 */
+			if (unlikely((cpu_buffer->commit_page !=
+				      cpu_buffer->tail_page) &&
+				     (cpu_buffer->commit_page ==
+				      cpu_buffer->reader_page))) {
+				local_inc(&cpu_buffer->commit_overrun);
+				goto out_reset;
+			}
+		}
+	}
+
+	rb_tail_page_update(cpu_buffer, tail_page, next_page);
+
+ out_again:
+
+	rb_reset_tail(cpu_buffer, tail, info);
+
+	/* Commit what we have for now. */
+	rb_end_commit(cpu_buffer);
+	/* rb_end_commit() decs committing */
+	local_inc(&cpu_buffer->committing);
+
+	/* fail and let the caller try again */
+	return ERR_PTR(-EAGAIN);
+
+ out_reset:
+	/* reset write */
+	rb_reset_tail(cpu_buffer, tail, info);
+
+	return NULL;
+}
+
+/* Slow path */
+static struct ring_buffer_event *
+rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
+{
+	if (abs)
+		event->type_len = RINGBUF_TYPE_TIME_STAMP;
+	else
+		event->type_len = RINGBUF_TYPE_TIME_EXTEND;
+
+	/* Not the first event on the page, or not delta? */
+	if (abs || rb_event_index(event)) {
+		event->time_delta = delta & TS_MASK;
+		event->array[0] = delta >> TS_SHIFT;
+	} else {
+		/* nope, just zero it */
+		event->time_delta = 0;
+		event->array[0] = 0;
+	}
+
+	return skip_time_extend(event);
+}
+
+#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+static inline bool sched_clock_stable(void)
+{
+	return true;
+}
+#endif
+
+static void
+rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
+		   struct rb_event_info *info)
+{
+	u64 write_stamp;
+
+	WARN_ONCE(1, "Delta way too big! %llu ts=%llu before=%llu after=%llu write stamp=%llu\n%s",
+		  (unsigned long long)info->delta,
+		  (unsigned long long)info->ts,
+		  (unsigned long long)info->before,
+		  (unsigned long long)info->after,
+		  (unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
+		  sched_clock_stable() ? "" :
+		  "If you just came from a suspend/resume,\n"
+		  "please switch to the trace global clock:\n"
+		  "  echo global > /sys/kernel/tracing/trace_clock\n"
+		  "or add trace_clock=global to the kernel command line\n");
+}
+
+static void rb_add_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
+				      struct ring_buffer_event **event,
+				      struct rb_event_info *info,
+				      u64 *delta,
+				      unsigned int *length)
+{
+	bool abs = info->add_timestamp &
+		(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
+
+	if (unlikely(info->delta > (1ULL << 59))) {
+		/*
+		 * Some timers can use more than 59 bits, and when a timestamp
+		 * is added to the buffer, it will lose those bits.
+		 */
+		if (abs && (info->ts & TS_MSB)) {
+			info->delta &= ABS_TS_MASK;
+
+		/* did the clock go backwards */
+		} else if (info->before == info->after && info->before > info->ts) {
+			/* not interrupted */
+			static int once;
+
+			/*
+			 * This is possible with a recalibrating of the TSC.
+			 * Do not produce a call stack, but just report it.
+			 */
+			if (!once) {
+				once++;
+				pr_warn("Ring buffer clock went backwards: %llu -> %llu\n",
+					info->before, info->ts);
+			}
+		} else
+			rb_check_timestamp(cpu_buffer, info);
+		if (!abs)
+			info->delta = 0;
+	}
+	*event = rb_add_time_stamp(*event, info->delta, abs);
+	*length -= RB_LEN_TIME_EXTEND;
+	*delta = 0;
+}
+
+/**
+ * rb_update_event - update event type and data
+ * @cpu_buffer: The per cpu buffer of the @event
+ * @event: the event to update
+ * @info: The info to update the @event with (contains length and delta)
+ *
+ * Update the type and data fields of the @event. The length
+ * is the actual size that is written to the ring buffer,
+ * and with this, we can determine what to place into the
+ * data field.
+ */
+static void
+rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
+		struct ring_buffer_event *event,
+		struct rb_event_info *info)
+{
+	unsigned length = info->length;
+	u64 delta = info->delta;
+	unsigned int nest = local_read(&cpu_buffer->committing) - 1;
+
+	if (!WARN_ON_ONCE(nest >= MAX_NEST))
+		cpu_buffer->event_stamp[nest] = info->ts;
+
+	/*
+	 * If we need to add a timestamp, then we
+	 * add it to the start of the reserved space.
+	 */
+	if (unlikely(info->add_timestamp))
+		rb_add_timestamp(cpu_buffer, &event, info, &delta, &length);
+
+	event->time_delta = delta;
+	length -= RB_EVNT_HDR_SIZE;
+	if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
+		event->type_len = 0;
+		event->array[0] = length;
+	} else
+		event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
+}
+
+static unsigned rb_calculate_event_length(unsigned length)
+{
+	struct ring_buffer_event event; /* Used only for sizeof array */
+
+	/* zero length can cause confusions */
+	if (!length)
+		length++;
+
+	if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
+		length += sizeof(event.array[0]);
+
+	length += RB_EVNT_HDR_SIZE;
+	length = ALIGN(length, RB_ARCH_ALIGNMENT);
+
+	/*
+	 * In case the time delta is larger than the 27 bits for it
+	 * in the header, we need to add a timestamp. If another
+	 * event comes in when trying to discard this one to increase
+	 * the length, then the timestamp will be added in the allocated
+	 * space of this event. If length is bigger than the size needed
+	 * for the TIME_EXTEND, then padding has to be used. The events
+	 * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
+	 * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
+	 * As length is a multiple of 4, we only need to worry if it
+	 * is 12 (RB_LEN_TIME_EXTEND + 4).
+	 */
+	if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
+		length += RB_ALIGNMENT;
+
+	return length;
+}
+
+static inline bool
+rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
+		  struct ring_buffer_event *event)
+{
+	unsigned long new_index, old_index;
+	struct buffer_page *bpage;
+	unsigned long addr;
+
+	new_index = rb_event_index(event);
+	old_index = new_index + rb_event_ts_length(event);
+	addr = (unsigned long)event;
+	addr &= PAGE_MASK;
+
+	bpage = READ_ONCE(cpu_buffer->tail_page);
+
+	/*
+	 * Make sure the tail_page is still the same and
+	 * the next write location is the end of this event
+	 */
+	if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
+		unsigned long write_mask =
+			local_read(&bpage->write) & ~RB_WRITE_MASK;
+		unsigned long event_length = rb_event_length(event);
+
+		/*
+		 * For the before_stamp to be different than the write_stamp
+		 * to make sure that the next event adds an absolute
+		 * value and does not rely on the saved write stamp, which
+		 * is now going to be bogus.
+		 *
+		 * By setting the before_stamp to zero, the next event
+		 * is not going to use the write_stamp and will instead
+		 * create an absolute timestamp. This means there's no
+		 * reason to update the wirte_stamp!
+		 */
+		rb_time_set(&cpu_buffer->before_stamp, 0);
+
+		/*
+		 * If an event were to come in now, it would see that the
+		 * write_stamp and the before_stamp are different, and assume
+		 * that this event just added itself before updating
+		 * the write stamp. The interrupting event will fix the
+		 * write stamp for us, and use an absolute timestamp.
+		 */
+
+		/*
+		 * This is on the tail page. It is possible that
+		 * a write could come in and move the tail page
+		 * and write to the next page. That is fine
+		 * because we just shorten what is on this page.
+		 */
+		old_index += write_mask;
+		new_index += write_mask;
+
+		/* caution: old_index gets updated on cmpxchg failure */
+		if (local_try_cmpxchg(&bpage->write, &old_index, new_index)) {
+			/* update counters */
+			local_sub(event_length, &cpu_buffer->entries_bytes);
+			return true;
+		}
+	}
+
+	/* could not discard */
+	return false;
+}
+
+static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	local_inc(&cpu_buffer->committing);
+	local_inc(&cpu_buffer->commits);
+}
+
+static __always_inline void
+rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	unsigned long max_count;
+
+	/*
+	 * We only race with interrupts and NMIs on this CPU.
+	 * If we own the commit event, then we can commit
+	 * all others that interrupted us, since the interruptions
+	 * are in stack format (they finish before they come
+	 * back to us). This allows us to do a simple loop to
+	 * assign the commit to the tail.
+	 */
+ again:
+	max_count = cpu_buffer->nr_pages * 100;
+
+	while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
+		if (RB_WARN_ON(cpu_buffer, !(--max_count)))
+			return;
+		if (RB_WARN_ON(cpu_buffer,
+			       rb_is_reader_page(cpu_buffer->tail_page)))
+			return;
+		/*
+		 * No need for a memory barrier here, as the update
+		 * of the tail_page did it for this page.
+		 */
+		local_set(&cpu_buffer->commit_page->page->commit,
+			  rb_page_write(cpu_buffer->commit_page));
+		rb_inc_page(&cpu_buffer->commit_page);
+		/* add barrier to keep gcc from optimizing too much */
+		barrier();
+	}
+	while (rb_commit_index(cpu_buffer) !=
+	       rb_page_write(cpu_buffer->commit_page)) {
+
+		/* Make sure the readers see the content of what is committed. */
+		smp_wmb();
+		local_set(&cpu_buffer->commit_page->page->commit,
+			  rb_page_write(cpu_buffer->commit_page));
+		RB_WARN_ON(cpu_buffer,
+			   local_read(&cpu_buffer->commit_page->page->commit) &
+			   ~RB_WRITE_MASK);
+		barrier();
+	}
+
+	/* again, keep gcc from optimizing */
+	barrier();
+
+	/*
+	 * If an interrupt came in just after the first while loop
+	 * and pushed the tail page forward, we will be left with
+	 * a dangling commit that will never go forward.
+	 */
+	if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
+		goto again;
+}
+
+static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	unsigned long commits;
+
+	if (RB_WARN_ON(cpu_buffer,
+		       !local_read(&cpu_buffer->committing)))
+		return;
+
+ again:
+	commits = local_read(&cpu_buffer->commits);
+	/* synchronize with interrupts */
+	barrier();
+	if (local_read(&cpu_buffer->committing) == 1)
+		rb_set_commit_to_write(cpu_buffer);
+
+	local_dec(&cpu_buffer->committing);
+
+	/* synchronize with interrupts */
+	barrier();
+
+	/*
+	 * Need to account for interrupts coming in between the
+	 * updating of the commit page and the clearing of the
+	 * committing counter.
+	 */
+	if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
+	    !local_read(&cpu_buffer->committing)) {
+		local_inc(&cpu_buffer->committing);
+		goto again;
+	}
+}
+
+static inline void rb_event_discard(struct ring_buffer_event *event)
+{
+	if (extended_time(event))
+		event = skip_time_extend(event);
+
+	/* array[0] holds the actual length for the discarded event */
+	event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
+	event->type_len = RINGBUF_TYPE_PADDING;
+	/* time delta must be non zero */
+	if (!event->time_delta)
+		event->time_delta = 1;
+}
+
+static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	local_inc(&cpu_buffer->entries);
+	rb_end_commit(cpu_buffer);
+}
+
+static __always_inline void
+rb_wakeups(struct trace_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
+{
+	if (buffer->irq_work.waiters_pending) {
+		buffer->irq_work.waiters_pending = false;
+		/* irq_work_queue() supplies it's own memory barriers */
+		irq_work_queue(&buffer->irq_work.work);
+	}
+
+	if (cpu_buffer->irq_work.waiters_pending) {
+		cpu_buffer->irq_work.waiters_pending = false;
+		/* irq_work_queue() supplies it's own memory barriers */
+		irq_work_queue(&cpu_buffer->irq_work.work);
+	}
+
+	if (cpu_buffer->last_pages_touch == local_read(&cpu_buffer->pages_touched))
+		return;
+
+	if (cpu_buffer->reader_page == cpu_buffer->commit_page)
+		return;
+
+	if (!cpu_buffer->irq_work.full_waiters_pending)
+		return;
+
+	cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
+
+	if (!full_hit(buffer, cpu_buffer->cpu, cpu_buffer->shortest_full))
+		return;
+
+	cpu_buffer->irq_work.wakeup_full = true;
+	cpu_buffer->irq_work.full_waiters_pending = false;
+	/* irq_work_queue() supplies it's own memory barriers */
+	irq_work_queue(&cpu_buffer->irq_work.work);
+}
+
+#ifdef CONFIG_RING_BUFFER_RECORD_RECURSION
+# define do_ring_buffer_record_recursion()	\
+	do_ftrace_record_recursion(_THIS_IP_, _RET_IP_)
+#else
+# define do_ring_buffer_record_recursion() do { } while (0)
+#endif
+
+/*
+ * The lock and unlock are done within a preempt disable section.
+ * The current_context per_cpu variable can only be modified
+ * by the current task between lock and unlock. But it can
+ * be modified more than once via an interrupt. To pass this
+ * information from the lock to the unlock without having to
+ * access the 'in_interrupt()' functions again (which do show
+ * a bit of overhead in something as critical as function tracing,
+ * we use a bitmask trick.
+ *
+ *  bit 1 =  NMI context
+ *  bit 2 =  IRQ context
+ *  bit 3 =  SoftIRQ context
+ *  bit 4 =  normal context.
+ *
+ * This works because this is the order of contexts that can
+ * preempt other contexts. A SoftIRQ never preempts an IRQ
+ * context.
+ *
+ * When the context is determined, the corresponding bit is
+ * checked and set (if it was set, then a recursion of that context
+ * happened).
+ *
+ * On unlock, we need to clear this bit. To do so, just subtract
+ * 1 from the current_context and AND it to itself.
+ *
+ * (binary)
+ *  101 - 1 = 100
+ *  101 & 100 = 100 (clearing bit zero)
+ *
+ *  1010 - 1 = 1001
+ *  1010 & 1001 = 1000 (clearing bit 1)
+ *
+ * The least significant bit can be cleared this way, and it
+ * just so happens that it is the same bit corresponding to
+ * the current context.
+ *
+ * Now the TRANSITION bit breaks the above slightly. The TRANSITION bit
+ * is set when a recursion is detected at the current context, and if
+ * the TRANSITION bit is already set, it will fail the recursion.
+ * This is needed because there's a lag between the changing of
+ * interrupt context and updating the preempt count. In this case,
+ * a false positive will be found. To handle this, one extra recursion
+ * is allowed, and this is done by the TRANSITION bit. If the TRANSITION
+ * bit is already set, then it is considered a recursion and the function
+ * ends. Otherwise, the TRANSITION bit is set, and that bit is returned.
+ *
+ * On the trace_recursive_unlock(), the TRANSITION bit will be the first
+ * to be cleared. Even if it wasn't the context that set it. That is,
+ * if an interrupt comes in while NORMAL bit is set and the ring buffer
+ * is called before preempt_count() is updated, since the check will
+ * be on the NORMAL bit, the TRANSITION bit will then be set. If an
+ * NMI then comes in, it will set the NMI bit, but when the NMI code
+ * does the trace_recursive_unlock() it will clear the TRANSITION bit
+ * and leave the NMI bit set. But this is fine, because the interrupt
+ * code that set the TRANSITION bit will then clear the NMI bit when it
+ * calls trace_recursive_unlock(). If another NMI comes in, it will
+ * set the TRANSITION bit and continue.
+ *
+ * Note: The TRANSITION bit only handles a single transition between context.
+ */
+
+static __always_inline bool
+trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	unsigned int val = cpu_buffer->current_context;
+	int bit = interrupt_context_level();
+
+	bit = RB_CTX_NORMAL - bit;
+
+	if (unlikely(val & (1 << (bit + cpu_buffer->nest)))) {
+		/*
+		 * It is possible that this was called by transitioning
+		 * between interrupt context, and preempt_count() has not
+		 * been updated yet. In this case, use the TRANSITION bit.
+		 */
+		bit = RB_CTX_TRANSITION;
+		if (val & (1 << (bit + cpu_buffer->nest))) {
+			do_ring_buffer_record_recursion();
+			return true;
+		}
+	}
+
+	val |= (1 << (bit + cpu_buffer->nest));
+	cpu_buffer->current_context = val;
+
+	return false;
+}
+
+static __always_inline void
+trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	cpu_buffer->current_context &=
+		cpu_buffer->current_context - (1 << cpu_buffer->nest);
+}
+
+/* The recursive locking above uses 5 bits */
+#define NESTED_BITS 5
+
+/**
+ * ring_buffer_nest_start - Allow to trace while nested
+ * @buffer: The ring buffer to modify
+ *
+ * The ring buffer has a safety mechanism to prevent recursion.
+ * But there may be a case where a trace needs to be done while
+ * tracing something else. In this case, calling this function
+ * will allow this function to nest within a currently active
+ * ring_buffer_lock_reserve().
+ *
+ * Call this function before calling another ring_buffer_lock_reserve() and
+ * call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit().
+ */
+void ring_buffer_nest_start(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	int cpu;
+
+	/* Enabled by ring_buffer_nest_end() */
+	preempt_disable_notrace();
+	cpu = raw_smp_processor_id();
+	cpu_buffer = buffer->buffers[cpu];
+	/* This is the shift value for the above recursive locking */
+	cpu_buffer->nest += NESTED_BITS;
+}
+
+/**
+ * ring_buffer_nest_end - Allow to trace while nested
+ * @buffer: The ring buffer to modify
+ *
+ * Must be called after ring_buffer_nest_start() and after the
+ * ring_buffer_unlock_commit().
+ */
+void ring_buffer_nest_end(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	int cpu;
+
+	/* disabled by ring_buffer_nest_start() */
+	cpu = raw_smp_processor_id();
+	cpu_buffer = buffer->buffers[cpu];
+	/* This is the shift value for the above recursive locking */
+	cpu_buffer->nest -= NESTED_BITS;
+	preempt_enable_notrace();
+}
+
+/**
+ * ring_buffer_unlock_commit - commit a reserved
+ * @buffer: The buffer to commit to
+ *
+ * This commits the data to the ring buffer, and releases any locks held.
+ *
+ * Must be paired with ring_buffer_lock_reserve.
+ */
+int ring_buffer_unlock_commit(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	int cpu = raw_smp_processor_id();
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	rb_commit(cpu_buffer);
+
+	rb_wakeups(buffer, cpu_buffer);
+
+	trace_recursive_unlock(cpu_buffer);
+
+	preempt_enable_notrace();
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
+
+/* Special value to validate all deltas on a page. */
+#define CHECK_FULL_PAGE		1L
+
+#ifdef CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS
+static void dump_buffer_page(struct buffer_data_page *bpage,
+			     struct rb_event_info *info,
+			     unsigned long tail)
+{
+	struct ring_buffer_event *event;
+	u64 ts, delta;
+	int e;
+
+	ts = bpage->time_stamp;
+	pr_warn("  [%lld] PAGE TIME STAMP\n", ts);
+
+	for (e = 0; e < tail; e += rb_event_length(event)) {
+
+		event = (struct ring_buffer_event *)(bpage->data + e);
+
+		switch (event->type_len) {
+
+		case RINGBUF_TYPE_TIME_EXTEND:
+			delta = rb_event_time_stamp(event);
+			ts += delta;
+			pr_warn("  [%lld] delta:%lld TIME EXTEND\n", ts, delta);
+			break;
+
+		case RINGBUF_TYPE_TIME_STAMP:
+			delta = rb_event_time_stamp(event);
+			ts = rb_fix_abs_ts(delta, ts);
+			pr_warn("  [%lld] absolute:%lld TIME STAMP\n", ts, delta);
+			break;
+
+		case RINGBUF_TYPE_PADDING:
+			ts += event->time_delta;
+			pr_warn("  [%lld] delta:%d PADDING\n", ts, event->time_delta);
+			break;
+
+		case RINGBUF_TYPE_DATA:
+			ts += event->time_delta;
+			pr_warn("  [%lld] delta:%d\n", ts, event->time_delta);
+			break;
+
+		default:
+			break;
+		}
+	}
+}
+
+static DEFINE_PER_CPU(atomic_t, checking);
+static atomic_t ts_dump;
+
+/*
+ * Check if the current event time stamp matches the deltas on
+ * the buffer page.
+ */
+static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
+			 struct rb_event_info *info,
+			 unsigned long tail)
+{
+	struct ring_buffer_event *event;
+	struct buffer_data_page *bpage;
+	u64 ts, delta;
+	bool full = false;
+	int e;
+
+	bpage = info->tail_page->page;
+
+	if (tail == CHECK_FULL_PAGE) {
+		full = true;
+		tail = local_read(&bpage->commit);
+	} else if (info->add_timestamp &
+		   (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE)) {
+		/* Ignore events with absolute time stamps */
+		return;
+	}
+
+	/*
+	 * Do not check the first event (skip possible extends too).
+	 * Also do not check if previous events have not been committed.
+	 */
+	if (tail <= 8 || tail > local_read(&bpage->commit))
+		return;
+
+	/*
+	 * If this interrupted another event,
+	 */
+	if (atomic_inc_return(this_cpu_ptr(&checking)) != 1)
+		goto out;
+
+	ts = bpage->time_stamp;
+
+	for (e = 0; e < tail; e += rb_event_length(event)) {
+
+		event = (struct ring_buffer_event *)(bpage->data + e);
+
+		switch (event->type_len) {
+
+		case RINGBUF_TYPE_TIME_EXTEND:
+			delta = rb_event_time_stamp(event);
+			ts += delta;
+			break;
+
+		case RINGBUF_TYPE_TIME_STAMP:
+			delta = rb_event_time_stamp(event);
+			ts = rb_fix_abs_ts(delta, ts);
+			break;
+
+		case RINGBUF_TYPE_PADDING:
+			if (event->time_delta == 1)
+				break;
+			fallthrough;
+		case RINGBUF_TYPE_DATA:
+			ts += event->time_delta;
+			break;
+
+		default:
+			RB_WARN_ON(cpu_buffer, 1);
+		}
+	}
+	if ((full && ts > info->ts) ||
+	    (!full && ts + info->delta != info->ts)) {
+		/* If another report is happening, ignore this one */
+		if (atomic_inc_return(&ts_dump) != 1) {
+			atomic_dec(&ts_dump);
+			goto out;
+		}
+		atomic_inc(&cpu_buffer->record_disabled);
+		/* There's some cases in boot up that this can happen */
+		WARN_ON_ONCE(system_state != SYSTEM_BOOTING);
+		pr_warn("[CPU: %d]TIME DOES NOT MATCH expected:%lld actual:%lld delta:%lld before:%lld after:%lld%s\n",
+			cpu_buffer->cpu,
+			ts + info->delta, info->ts, info->delta,
+			info->before, info->after,
+			full ? " (full)" : "");
+		dump_buffer_page(bpage, info, tail);
+		atomic_dec(&ts_dump);
+		/* Do not re-enable checking */
+		return;
+	}
+out:
+	atomic_dec(this_cpu_ptr(&checking));
+}
+#else
+static inline void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
+			 struct rb_event_info *info,
+			 unsigned long tail)
+{
+}
+#endif /* CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS */
+
+static struct ring_buffer_event *
+__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
+		  struct rb_event_info *info)
+{
+	struct ring_buffer_event *event;
+	struct buffer_page *tail_page;
+	unsigned long tail, write, w;
+	bool a_ok;
+	bool b_ok;
+
+	/* Don't let the compiler play games with cpu_buffer->tail_page */
+	tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
+
+ /*A*/	w = local_read(&tail_page->write) & RB_WRITE_MASK;
+	barrier();
+	b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
+	a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
+	barrier();
+	info->ts = rb_time_stamp(cpu_buffer->buffer);
+
+	if ((info->add_timestamp & RB_ADD_STAMP_ABSOLUTE)) {
+		info->delta = info->ts;
+	} else {
+		/*
+		 * If interrupting an event time update, we may need an
+		 * absolute timestamp.
+		 * Don't bother if this is the start of a new page (w == 0).
+		 */
+		if (!w) {
+			/* Use the sub-buffer timestamp */
+			info->delta = 0;
+		} else if (unlikely(!a_ok || !b_ok || info->before != info->after)) {
+			info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
+			info->length += RB_LEN_TIME_EXTEND;
+		} else {
+			info->delta = info->ts - info->after;
+			if (unlikely(test_time_stamp(info->delta))) {
+				info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+				info->length += RB_LEN_TIME_EXTEND;
+			}
+		}
+	}
+
+ /*B*/	rb_time_set(&cpu_buffer->before_stamp, info->ts);
+
+ /*C*/	write = local_add_return(info->length, &tail_page->write);
+
+	/* set write to only the index of the write */
+	write &= RB_WRITE_MASK;
+
+	tail = write - info->length;
+
+	/* See if we shot pass the end of this buffer page */
+	if (unlikely(write > BUF_PAGE_SIZE)) {
+		check_buffer(cpu_buffer, info, CHECK_FULL_PAGE);
+		return rb_move_tail(cpu_buffer, tail, info);
+	}
+
+	if (likely(tail == w)) {
+		/* Nothing interrupted us between A and C */
+ /*D*/		rb_time_set(&cpu_buffer->write_stamp, info->ts);
+		/*
+		 * If something came in between C and D, the write stamp
+		 * may now not be in sync. But that's fine as the before_stamp
+		 * will be different and then next event will just be forced
+		 * to use an absolute timestamp.
+		 */
+		if (likely(!(info->add_timestamp &
+			     (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
+			/* This did not interrupt any time update */
+			info->delta = info->ts - info->after;
+		else
+			/* Just use full timestamp for interrupting event */
+			info->delta = info->ts;
+		check_buffer(cpu_buffer, info, tail);
+	} else {
+		u64 ts;
+		/* SLOW PATH - Interrupted between A and C */
+
+		/* Save the old before_stamp */
+		a_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
+		RB_WARN_ON(cpu_buffer, !a_ok);
+
+		/*
+		 * Read a new timestamp and update the before_stamp to make
+		 * the next event after this one force using an absolute
+		 * timestamp. This is in case an interrupt were to come in
+		 * between E and F.
+		 */
+		ts = rb_time_stamp(cpu_buffer->buffer);
+		rb_time_set(&cpu_buffer->before_stamp, ts);
+
+		barrier();
+ /*E*/		a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
+		/* Was interrupted before here, write_stamp must be valid */
+		RB_WARN_ON(cpu_buffer, !a_ok);
+		barrier();
+ /*F*/		if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
+		    info->after == info->before && info->after < ts) {
+			/*
+			 * Nothing came after this event between C and F, it is
+			 * safe to use info->after for the delta as it
+			 * matched info->before and is still valid.
+			 */
+			info->delta = ts - info->after;
+		} else {
+			/*
+			 * Interrupted between C and F:
+			 * Lost the previous events time stamp. Just set the
+			 * delta to zero, and this will be the same time as
+			 * the event this event interrupted. And the events that
+			 * came after this will still be correct (as they would
+			 * have built their delta on the previous event.
+			 */
+			info->delta = 0;
+		}
+		info->ts = ts;
+		info->add_timestamp &= ~RB_ADD_STAMP_FORCE;
+	}
+
+	/*
+	 * If this is the first commit on the page, then it has the same
+	 * timestamp as the page itself.
+	 */
+	if (unlikely(!tail && !(info->add_timestamp &
+				(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
+		info->delta = 0;
+
+	/* We reserved something on the buffer */
+
+	event = __rb_page_index(tail_page, tail);
+	rb_update_event(cpu_buffer, event, info);
+
+	local_inc(&tail_page->entries);
+
+	/*
+	 * If this is the first commit on the page, then update
+	 * its timestamp.
+	 */
+	if (unlikely(!tail))
+		tail_page->page->time_stamp = info->ts;
+
+	/* account for these added bytes */
+	local_add(info->length, &cpu_buffer->entries_bytes);
+
+	return event;
+}
+
+static __always_inline struct ring_buffer_event *
+rb_reserve_next_event(struct trace_buffer *buffer,
+		      struct ring_buffer_per_cpu *cpu_buffer,
+		      unsigned long length)
+{
+	struct ring_buffer_event *event;
+	struct rb_event_info info;
+	int nr_loops = 0;
+	int add_ts_default;
+
+	/* ring buffer does cmpxchg, make sure it is safe in NMI context */
+	if (!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) &&
+	    (unlikely(in_nmi()))) {
+		return NULL;
+	}
+
+	rb_start_commit(cpu_buffer);
+	/* The commit page can not change after this */
+
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
+	/*
+	 * Due to the ability to swap a cpu buffer from a buffer
+	 * it is possible it was swapped before we committed.
+	 * (committing stops a swap). We check for it here and
+	 * if it happened, we have to fail the write.
+	 */
+	barrier();
+	if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
+		local_dec(&cpu_buffer->committing);
+		local_dec(&cpu_buffer->commits);
+		return NULL;
+	}
+#endif
+
+	info.length = rb_calculate_event_length(length);
+
+	if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
+		add_ts_default = RB_ADD_STAMP_ABSOLUTE;
+		info.length += RB_LEN_TIME_EXTEND;
+		if (info.length > BUF_MAX_DATA_SIZE)
+			goto out_fail;
+	} else {
+		add_ts_default = RB_ADD_STAMP_NONE;
+	}
+
+ again:
+	info.add_timestamp = add_ts_default;
+	info.delta = 0;
+
+	/*
+	 * We allow for interrupts to reenter here and do a trace.
+	 * If one does, it will cause this original code to loop
+	 * back here. Even with heavy interrupts happening, this
+	 * should only happen a few times in a row. If this happens
+	 * 1000 times in a row, there must be either an interrupt
+	 * storm or we have something buggy.
+	 * Bail!
+	 */
+	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
+		goto out_fail;
+
+	event = __rb_reserve_next(cpu_buffer, &info);
+
+	if (unlikely(PTR_ERR(event) == -EAGAIN)) {
+		if (info.add_timestamp & (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND))
+			info.length -= RB_LEN_TIME_EXTEND;
+		goto again;
+	}
+
+	if (likely(event))
+		return event;
+ out_fail:
+	rb_end_commit(cpu_buffer);
+	return NULL;
+}
+
+/**
+ * ring_buffer_lock_reserve - reserve a part of the buffer
+ * @buffer: the ring buffer to reserve from
+ * @length: the length of the data to reserve (excluding event header)
+ *
+ * Returns a reserved event on the ring buffer to copy directly to.
+ * The user of this interface will need to get the body to write into
+ * and can use the ring_buffer_event_data() interface.
+ *
+ * The length is the length of the data needed, not the event length
+ * which also includes the event header.
+ *
+ * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
+ * If NULL is returned, then nothing has been allocated or locked.
+ */
+struct ring_buffer_event *
+ring_buffer_lock_reserve(struct trace_buffer *buffer, unsigned long length)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_event *event;
+	int cpu;
+
+	/* If we are tracing schedule, we don't want to recurse */
+	preempt_disable_notrace();
+
+	if (unlikely(atomic_read(&buffer->record_disabled)))
+		goto out;
+
+	cpu = raw_smp_processor_id();
+
+	if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
+		goto out;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
+		goto out;
+
+	if (unlikely(length > BUF_MAX_DATA_SIZE))
+		goto out;
+
+	if (unlikely(trace_recursive_lock(cpu_buffer)))
+		goto out;
+
+	event = rb_reserve_next_event(buffer, cpu_buffer, length);
+	if (!event)
+		goto out_unlock;
+
+	return event;
+
+ out_unlock:
+	trace_recursive_unlock(cpu_buffer);
+ out:
+	preempt_enable_notrace();
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
+
+/*
+ * Decrement the entries to the page that an event is on.
+ * The event does not even need to exist, only the pointer
+ * to the page it is on. This may only be called before the commit
+ * takes place.
+ */
+static inline void
+rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
+		   struct ring_buffer_event *event)
+{
+	unsigned long addr = (unsigned long)event;
+	struct buffer_page *bpage = cpu_buffer->commit_page;
+	struct buffer_page *start;
+
+	addr &= PAGE_MASK;
+
+	/* Do the likely case first */
+	if (likely(bpage->page == (void *)addr)) {
+		local_dec(&bpage->entries);
+		return;
+	}
+
+	/*
+	 * Because the commit page may be on the reader page we
+	 * start with the next page and check the end loop there.
+	 */
+	rb_inc_page(&bpage);
+	start = bpage;
+	do {
+		if (bpage->page == (void *)addr) {
+			local_dec(&bpage->entries);
+			return;
+		}
+		rb_inc_page(&bpage);
+	} while (bpage != start);
+
+	/* commit not part of this buffer?? */
+	RB_WARN_ON(cpu_buffer, 1);
+}
+
+/**
+ * ring_buffer_discard_commit - discard an event that has not been committed
+ * @buffer: the ring buffer
+ * @event: non committed event to discard
+ *
+ * Sometimes an event that is in the ring buffer needs to be ignored.
+ * This function lets the user discard an event in the ring buffer
+ * and then that event will not be read later.
+ *
+ * This function only works if it is called before the item has been
+ * committed. It will try to free the event from the ring buffer
+ * if another event has not been added behind it.
+ *
+ * If another event has been added behind it, it will set the event
+ * up as discarded, and perform the commit.
+ *
+ * If this function is called, do not call ring_buffer_unlock_commit on
+ * the event.
+ */
+void ring_buffer_discard_commit(struct trace_buffer *buffer,
+				struct ring_buffer_event *event)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	int cpu;
+
+	/* The event is discarded regardless */
+	rb_event_discard(event);
+
+	cpu = smp_processor_id();
+	cpu_buffer = buffer->buffers[cpu];
+
+	/*
+	 * This must only be called if the event has not been
+	 * committed yet. Thus we can assume that preemption
+	 * is still disabled.
+	 */
+	RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
+
+	rb_decrement_entry(cpu_buffer, event);
+	if (rb_try_to_discard(cpu_buffer, event))
+		goto out;
+
+ out:
+	rb_end_commit(cpu_buffer);
+
+	trace_recursive_unlock(cpu_buffer);
+
+	preempt_enable_notrace();
+
+}
+EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
+
+/**
+ * ring_buffer_write - write data to the buffer without reserving
+ * @buffer: The ring buffer to write to.
+ * @length: The length of the data being written (excluding the event header)
+ * @data: The data to write to the buffer.
+ *
+ * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
+ * one function. If you already have the data to write to the buffer, it
+ * may be easier to simply call this function.
+ *
+ * Note, like ring_buffer_lock_reserve, the length is the length of the data
+ * and not the length of the event which would hold the header.
+ */
+int ring_buffer_write(struct trace_buffer *buffer,
+		      unsigned long length,
+		      void *data)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_event *event;
+	void *body;
+	int ret = -EBUSY;
+	int cpu;
+
+	preempt_disable_notrace();
+
+	if (atomic_read(&buffer->record_disabled))
+		goto out;
+
+	cpu = raw_smp_processor_id();
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		goto out;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	if (atomic_read(&cpu_buffer->record_disabled))
+		goto out;
+
+	if (length > BUF_MAX_DATA_SIZE)
+		goto out;
+
+	if (unlikely(trace_recursive_lock(cpu_buffer)))
+		goto out;
+
+	event = rb_reserve_next_event(buffer, cpu_buffer, length);
+	if (!event)
+		goto out_unlock;
+
+	body = rb_event_data(event);
+
+	memcpy(body, data, length);
+
+	rb_commit(cpu_buffer);
+
+	rb_wakeups(buffer, cpu_buffer);
+
+	ret = 0;
+
+ out_unlock:
+	trace_recursive_unlock(cpu_buffer);
+
+ out:
+	preempt_enable_notrace();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_write);
+
+static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct buffer_page *reader = cpu_buffer->reader_page;
+	struct buffer_page *head = rb_set_head_page(cpu_buffer);
+	struct buffer_page *commit = cpu_buffer->commit_page;
+
+	/* In case of error, head will be NULL */
+	if (unlikely(!head))
+		return true;
+
+	/* Reader should exhaust content in reader page */
+	if (reader->read != rb_page_commit(reader))
+		return false;
+
+	/*
+	 * If writers are committing on the reader page, knowing all
+	 * committed content has been read, the ring buffer is empty.
+	 */
+	if (commit == reader)
+		return true;
+
+	/*
+	 * If writers are committing on a page other than reader page
+	 * and head page, there should always be content to read.
+	 */
+	if (commit != head)
+		return false;
+
+	/*
+	 * Writers are committing on the head page, we just need
+	 * to care about there're committed data, and the reader will
+	 * swap reader page with head page when it is to read data.
+	 */
+	return rb_page_commit(commit) == 0;
+}
+
+/**
+ * ring_buffer_record_disable - stop all writes into the buffer
+ * @buffer: The ring buffer to stop writes to.
+ *
+ * This prevents all writes to the buffer. Any attempt to write
+ * to the buffer after this will fail and return NULL.
+ *
+ * The caller should call synchronize_rcu() after this.
+ */
+void ring_buffer_record_disable(struct trace_buffer *buffer)
+{
+	atomic_inc(&buffer->record_disabled);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
+
+/**
+ * ring_buffer_record_enable - enable writes to the buffer
+ * @buffer: The ring buffer to enable writes
+ *
+ * Note, multiple disables will need the same number of enables
+ * to truly enable the writing (much like preempt_disable).
+ */
+void ring_buffer_record_enable(struct trace_buffer *buffer)
+{
+	atomic_dec(&buffer->record_disabled);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
+
+/**
+ * ring_buffer_record_off - stop all writes into the buffer
+ * @buffer: The ring buffer to stop writes to.
+ *
+ * This prevents all writes to the buffer. Any attempt to write
+ * to the buffer after this will fail and return NULL.
+ *
+ * This is different than ring_buffer_record_disable() as
+ * it works like an on/off switch, where as the disable() version
+ * must be paired with a enable().
+ */
+void ring_buffer_record_off(struct trace_buffer *buffer)
+{
+	unsigned int rd;
+	unsigned int new_rd;
+
+	rd = atomic_read(&buffer->record_disabled);
+	do {
+		new_rd = rd | RB_BUFFER_OFF;
+	} while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd));
+}
+EXPORT_SYMBOL_GPL(ring_buffer_record_off);
+
+/**
+ * ring_buffer_record_on - restart writes into the buffer
+ * @buffer: The ring buffer to start writes to.
+ *
+ * This enables all writes to the buffer that was disabled by
+ * ring_buffer_record_off().
+ *
+ * This is different than ring_buffer_record_enable() as
+ * it works like an on/off switch, where as the enable() version
+ * must be paired with a disable().
+ */
+void ring_buffer_record_on(struct trace_buffer *buffer)
+{
+	unsigned int rd;
+	unsigned int new_rd;
+
+	rd = atomic_read(&buffer->record_disabled);
+	do {
+		new_rd = rd & ~RB_BUFFER_OFF;
+	} while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd));
+}
+EXPORT_SYMBOL_GPL(ring_buffer_record_on);
+
+/**
+ * ring_buffer_record_is_on - return true if the ring buffer can write
+ * @buffer: The ring buffer to see if write is enabled
+ *
+ * Returns true if the ring buffer is in a state that it accepts writes.
+ */
+bool ring_buffer_record_is_on(struct trace_buffer *buffer)
+{
+	return !atomic_read(&buffer->record_disabled);
+}
+
+/**
+ * ring_buffer_record_is_set_on - return true if the ring buffer is set writable
+ * @buffer: The ring buffer to see if write is set enabled
+ *
+ * Returns true if the ring buffer is set writable by ring_buffer_record_on().
+ * Note that this does NOT mean it is in a writable state.
+ *
+ * It may return true when the ring buffer has been disabled by
+ * ring_buffer_record_disable(), as that is a temporary disabling of
+ * the ring buffer.
+ */
+bool ring_buffer_record_is_set_on(struct trace_buffer *buffer)
+{
+	return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
+}
+
+/**
+ * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
+ * @buffer: The ring buffer to stop writes to.
+ * @cpu: The CPU buffer to stop
+ *
+ * This prevents all writes to the buffer. Any attempt to write
+ * to the buffer after this will fail and return NULL.
+ *
+ * The caller should call synchronize_rcu() after this.
+ */
+void ring_buffer_record_disable_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return;
+
+	cpu_buffer = buffer->buffers[cpu];
+	atomic_inc(&cpu_buffer->record_disabled);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
+
+/**
+ * ring_buffer_record_enable_cpu - enable writes to the buffer
+ * @buffer: The ring buffer to enable writes
+ * @cpu: The CPU to enable.
+ *
+ * Note, multiple disables will need the same number of enables
+ * to truly enable the writing (much like preempt_disable).
+ */
+void ring_buffer_record_enable_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return;
+
+	cpu_buffer = buffer->buffers[cpu];
+	atomic_dec(&cpu_buffer->record_disabled);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
+
+/*
+ * The total entries in the ring buffer is the running counter
+ * of entries entered into the ring buffer, minus the sum of
+ * the entries read from the ring buffer and the number of
+ * entries that were overwritten.
+ */
+static inline unsigned long
+rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	return local_read(&cpu_buffer->entries) -
+		(local_read(&cpu_buffer->overrun) + cpu_buffer->read);
+}
+
+/**
+ * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to read from.
+ */
+u64 ring_buffer_oldest_event_ts(struct trace_buffer *buffer, int cpu)
+{
+	unsigned long flags;
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct buffer_page *bpage;
+	u64 ret = 0;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	/*
+	 * if the tail is on reader_page, oldest time stamp is on the reader
+	 * page
+	 */
+	if (cpu_buffer->tail_page == cpu_buffer->reader_page)
+		bpage = cpu_buffer->reader_page;
+	else
+		bpage = rb_set_head_page(cpu_buffer);
+	if (bpage)
+		ret = bpage->page->time_stamp;
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
+
+/**
+ * ring_buffer_bytes_cpu - get the number of bytes unconsumed in a cpu buffer
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to read from.
+ */
+unsigned long ring_buffer_bytes_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+	ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
+
+/**
+ * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the entries from.
+ */
+unsigned long ring_buffer_entries_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	return rb_num_of_entries(cpu_buffer);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
+
+/**
+ * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
+ * buffer wrapping around (only if RB_FL_OVERWRITE is on).
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the number of overruns from
+ */
+unsigned long ring_buffer_overrun_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+	ret = local_read(&cpu_buffer->overrun);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
+
+/**
+ * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
+ * commits failing due to the buffer wrapping around while there are uncommitted
+ * events, such as during an interrupt storm.
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the number of overruns from
+ */
+unsigned long
+ring_buffer_commit_overrun_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+	ret = local_read(&cpu_buffer->commit_overrun);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
+
+/**
+ * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
+ * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the number of overruns from
+ */
+unsigned long
+ring_buffer_dropped_events_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+	ret = local_read(&cpu_buffer->dropped_events);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
+
+/**
+ * ring_buffer_read_events_cpu - get the number of events successfully read
+ * @buffer: The ring buffer
+ * @cpu: The per CPU buffer to get the number of events read
+ */
+unsigned long
+ring_buffer_read_events_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	cpu_buffer = buffer->buffers[cpu];
+	return cpu_buffer->read;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
+
+/**
+ * ring_buffer_entries - get the number of entries in a buffer
+ * @buffer: The ring buffer
+ *
+ * Returns the total number of entries in the ring buffer
+ * (all CPU entries)
+ */
+unsigned long ring_buffer_entries(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long entries = 0;
+	int cpu;
+
+	/* if you care about this being correct, lock the buffer */
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+		entries += rb_num_of_entries(cpu_buffer);
+	}
+
+	return entries;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_entries);
+
+/**
+ * ring_buffer_overruns - get the number of overruns in buffer
+ * @buffer: The ring buffer
+ *
+ * Returns the total number of overruns in the ring buffer
+ * (all CPU entries)
+ */
+unsigned long ring_buffer_overruns(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long overruns = 0;
+	int cpu;
+
+	/* if you care about this being correct, lock the buffer */
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+		overruns += local_read(&cpu_buffer->overrun);
+	}
+
+	return overruns;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_overruns);
+
+static void rb_iter_reset(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+
+	/* Iterator usage is expected to have record disabled */
+	iter->head_page = cpu_buffer->reader_page;
+	iter->head = cpu_buffer->reader_page->read;
+	iter->next_event = iter->head;
+
+	iter->cache_reader_page = iter->head_page;
+	iter->cache_read = cpu_buffer->read;
+	iter->cache_pages_removed = cpu_buffer->pages_removed;
+
+	if (iter->head) {
+		iter->read_stamp = cpu_buffer->read_stamp;
+		iter->page_stamp = cpu_buffer->reader_page->page->time_stamp;
+	} else {
+		iter->read_stamp = iter->head_page->page->time_stamp;
+		iter->page_stamp = iter->read_stamp;
+	}
+}
+
+/**
+ * ring_buffer_iter_reset - reset an iterator
+ * @iter: The iterator to reset
+ *
+ * Resets the iterator, so that it will start from the beginning
+ * again.
+ */
+void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags;
+
+	if (!iter)
+		return;
+
+	cpu_buffer = iter->cpu_buffer;
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	rb_iter_reset(iter);
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
+
+/**
+ * ring_buffer_iter_empty - check if an iterator has no more to read
+ * @iter: The iterator to check
+ */
+int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct buffer_page *reader;
+	struct buffer_page *head_page;
+	struct buffer_page *commit_page;
+	struct buffer_page *curr_commit_page;
+	unsigned commit;
+	u64 curr_commit_ts;
+	u64 commit_ts;
+
+	cpu_buffer = iter->cpu_buffer;
+	reader = cpu_buffer->reader_page;
+	head_page = cpu_buffer->head_page;
+	commit_page = cpu_buffer->commit_page;
+	commit_ts = commit_page->page->time_stamp;
+
+	/*
+	 * When the writer goes across pages, it issues a cmpxchg which
+	 * is a mb(), which will synchronize with the rmb here.
+	 * (see rb_tail_page_update())
+	 */
+	smp_rmb();
+	commit = rb_page_commit(commit_page);
+	/* We want to make sure that the commit page doesn't change */
+	smp_rmb();
+
+	/* Make sure commit page didn't change */
+	curr_commit_page = READ_ONCE(cpu_buffer->commit_page);
+	curr_commit_ts = READ_ONCE(curr_commit_page->page->time_stamp);
+
+	/* If the commit page changed, then there's more data */
+	if (curr_commit_page != commit_page ||
+	    curr_commit_ts != commit_ts)
+		return 0;
+
+	/* Still racy, as it may return a false positive, but that's OK */
+	return ((iter->head_page == commit_page && iter->head >= commit) ||
+		(iter->head_page == reader && commit_page == head_page &&
+		 head_page->read == commit &&
+		 iter->head == rb_page_commit(cpu_buffer->reader_page)));
+}
+EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
+
+static void
+rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
+		     struct ring_buffer_event *event)
+{
+	u64 delta;
+
+	switch (event->type_len) {
+	case RINGBUF_TYPE_PADDING:
+		return;
+
+	case RINGBUF_TYPE_TIME_EXTEND:
+		delta = rb_event_time_stamp(event);
+		cpu_buffer->read_stamp += delta;
+		return;
+
+	case RINGBUF_TYPE_TIME_STAMP:
+		delta = rb_event_time_stamp(event);
+		delta = rb_fix_abs_ts(delta, cpu_buffer->read_stamp);
+		cpu_buffer->read_stamp = delta;
+		return;
+
+	case RINGBUF_TYPE_DATA:
+		cpu_buffer->read_stamp += event->time_delta;
+		return;
+
+	default:
+		RB_WARN_ON(cpu_buffer, 1);
+	}
+}
+
+static void
+rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
+			  struct ring_buffer_event *event)
+{
+	u64 delta;
+
+	switch (event->type_len) {
+	case RINGBUF_TYPE_PADDING:
+		return;
+
+	case RINGBUF_TYPE_TIME_EXTEND:
+		delta = rb_event_time_stamp(event);
+		iter->read_stamp += delta;
+		return;
+
+	case RINGBUF_TYPE_TIME_STAMP:
+		delta = rb_event_time_stamp(event);
+		delta = rb_fix_abs_ts(delta, iter->read_stamp);
+		iter->read_stamp = delta;
+		return;
+
+	case RINGBUF_TYPE_DATA:
+		iter->read_stamp += event->time_delta;
+		return;
+
+	default:
+		RB_WARN_ON(iter->cpu_buffer, 1);
+	}
+}
+
+static struct buffer_page *
+rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct buffer_page *reader = NULL;
+	unsigned long overwrite;
+	unsigned long flags;
+	int nr_loops = 0;
+	bool ret;
+
+	local_irq_save(flags);
+	arch_spin_lock(&cpu_buffer->lock);
+
+ again:
+	/*
+	 * This should normally only loop twice. But because the
+	 * start of the reader inserts an empty page, it causes
+	 * a case where we will loop three times. There should be no
+	 * reason to loop four times (that I know of).
+	 */
+	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
+		reader = NULL;
+		goto out;
+	}
+
+	reader = cpu_buffer->reader_page;
+
+	/* If there's more to read, return this page */
+	if (cpu_buffer->reader_page->read < rb_page_size(reader))
+		goto out;
+
+	/* Never should we have an index greater than the size */
+	if (RB_WARN_ON(cpu_buffer,
+		       cpu_buffer->reader_page->read > rb_page_size(reader)))
+		goto out;
+
+	/* check if we caught up to the tail */
+	reader = NULL;
+	if (cpu_buffer->commit_page == cpu_buffer->reader_page)
+		goto out;
+
+	/* Don't bother swapping if the ring buffer is empty */
+	if (rb_num_of_entries(cpu_buffer) == 0)
+		goto out;
+
+	/*
+	 * Reset the reader page to size zero.
+	 */
+	local_set(&cpu_buffer->reader_page->write, 0);
+	local_set(&cpu_buffer->reader_page->entries, 0);
+	local_set(&cpu_buffer->reader_page->page->commit, 0);
+	cpu_buffer->reader_page->real_end = 0;
+
+ spin:
+	/*
+	 * Splice the empty reader page into the list around the head.
+	 */
+	reader = rb_set_head_page(cpu_buffer);
+	if (!reader)
+		goto out;
+	cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
+	cpu_buffer->reader_page->list.prev = reader->list.prev;
+
+	/*
+	 * cpu_buffer->pages just needs to point to the buffer, it
+	 *  has no specific buffer page to point to. Lets move it out
+	 *  of our way so we don't accidentally swap it.
+	 */
+	cpu_buffer->pages = reader->list.prev;
+
+	/* The reader page will be pointing to the new head */
+	rb_set_list_to_head(&cpu_buffer->reader_page->list);
+
+	/*
+	 * We want to make sure we read the overruns after we set up our
+	 * pointers to the next object. The writer side does a
+	 * cmpxchg to cross pages which acts as the mb on the writer
+	 * side. Note, the reader will constantly fail the swap
+	 * while the writer is updating the pointers, so this
+	 * guarantees that the overwrite recorded here is the one we
+	 * want to compare with the last_overrun.
+	 */
+	smp_mb();
+	overwrite = local_read(&(cpu_buffer->overrun));
+
+	/*
+	 * Here's the tricky part.
+	 *
+	 * We need to move the pointer past the header page.
+	 * But we can only do that if a writer is not currently
+	 * moving it. The page before the header page has the
+	 * flag bit '1' set if it is pointing to the page we want.
+	 * but if the writer is in the process of moving it
+	 * than it will be '2' or already moved '0'.
+	 */
+
+	ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
+
+	/*
+	 * If we did not convert it, then we must try again.
+	 */
+	if (!ret)
+		goto spin;
+
+	/*
+	 * Yay! We succeeded in replacing the page.
+	 *
+	 * Now make the new head point back to the reader page.
+	 */
+	rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
+	rb_inc_page(&cpu_buffer->head_page);
+
+	local_inc(&cpu_buffer->pages_read);
+
+	/* Finally update the reader page to the new head */
+	cpu_buffer->reader_page = reader;
+	cpu_buffer->reader_page->read = 0;
+
+	if (overwrite != cpu_buffer->last_overrun) {
+		cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
+		cpu_buffer->last_overrun = overwrite;
+	}
+
+	goto again;
+
+ out:
+	/* Update the read_stamp on the first event */
+	if (reader && reader->read == 0)
+		cpu_buffer->read_stamp = reader->page->time_stamp;
+
+	arch_spin_unlock(&cpu_buffer->lock);
+	local_irq_restore(flags);
+
+	/*
+	 * The writer has preempt disable, wait for it. But not forever
+	 * Although, 1 second is pretty much "forever"
+	 */
+#define USECS_WAIT	1000000
+        for (nr_loops = 0; nr_loops < USECS_WAIT; nr_loops++) {
+		/* If the write is past the end of page, a writer is still updating it */
+		if (likely(!reader || rb_page_write(reader) <= BUF_PAGE_SIZE))
+			break;
+
+		udelay(1);
+
+		/* Get the latest version of the reader write value */
+		smp_rmb();
+	}
+
+	/* The writer is not moving forward? Something is wrong */
+	if (RB_WARN_ON(cpu_buffer, nr_loops == USECS_WAIT))
+		reader = NULL;
+
+	/*
+	 * Make sure we see any padding after the write update
+	 * (see rb_reset_tail()).
+	 *
+	 * In addition, a writer may be writing on the reader page
+	 * if the page has not been fully filled, so the read barrier
+	 * is also needed to make sure we see the content of what is
+	 * committed by the writer (see rb_set_commit_to_write()).
+	 */
+	smp_rmb();
+
+
+	return reader;
+}
+
+static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct ring_buffer_event *event;
+	struct buffer_page *reader;
+	unsigned length;
+
+	reader = rb_get_reader_page(cpu_buffer);
+
+	/* This function should not be called when buffer is empty */
+	if (RB_WARN_ON(cpu_buffer, !reader))
+		return;
+
+	event = rb_reader_event(cpu_buffer);
+
+	if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
+		cpu_buffer->read++;
+
+	rb_update_read_stamp(cpu_buffer, event);
+
+	length = rb_event_length(event);
+	cpu_buffer->reader_page->read += length;
+	cpu_buffer->read_bytes += length;
+}
+
+static void rb_advance_iter(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	cpu_buffer = iter->cpu_buffer;
+
+	/* If head == next_event then we need to jump to the next event */
+	if (iter->head == iter->next_event) {
+		/* If the event gets overwritten again, there's nothing to do */
+		if (rb_iter_head_event(iter) == NULL)
+			return;
+	}
+
+	iter->head = iter->next_event;
+
+	/*
+	 * Check if we are at the end of the buffer.
+	 */
+	if (iter->next_event >= rb_page_size(iter->head_page)) {
+		/* discarded commits can make the page empty */
+		if (iter->head_page == cpu_buffer->commit_page)
+			return;
+		rb_inc_iter(iter);
+		return;
+	}
+
+	rb_update_iter_read_stamp(iter, iter->event);
+}
+
+static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	return cpu_buffer->lost_events;
+}
+
+static struct ring_buffer_event *
+rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
+	       unsigned long *lost_events)
+{
+	struct ring_buffer_event *event;
+	struct buffer_page *reader;
+	int nr_loops = 0;
+
+	if (ts)
+		*ts = 0;
+ again:
+	/*
+	 * We repeat when a time extend is encountered.
+	 * Since the time extend is always attached to a data event,
+	 * we should never loop more than once.
+	 * (We never hit the following condition more than twice).
+	 */
+	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
+		return NULL;
+
+	reader = rb_get_reader_page(cpu_buffer);
+	if (!reader)
+		return NULL;
+
+	event = rb_reader_event(cpu_buffer);
+
+	switch (event->type_len) {
+	case RINGBUF_TYPE_PADDING:
+		if (rb_null_event(event))
+			RB_WARN_ON(cpu_buffer, 1);
+		/*
+		 * Because the writer could be discarding every
+		 * event it creates (which would probably be bad)
+		 * if we were to go back to "again" then we may never
+		 * catch up, and will trigger the warn on, or lock
+		 * the box. Return the padding, and we will release
+		 * the current locks, and try again.
+		 */
+		return event;
+
+	case RINGBUF_TYPE_TIME_EXTEND:
+		/* Internal data, OK to advance */
+		rb_advance_reader(cpu_buffer);
+		goto again;
+
+	case RINGBUF_TYPE_TIME_STAMP:
+		if (ts) {
+			*ts = rb_event_time_stamp(event);
+			*ts = rb_fix_abs_ts(*ts, reader->page->time_stamp);
+			ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
+							 cpu_buffer->cpu, ts);
+		}
+		/* Internal data, OK to advance */
+		rb_advance_reader(cpu_buffer);
+		goto again;
+
+	case RINGBUF_TYPE_DATA:
+		if (ts && !(*ts)) {
+			*ts = cpu_buffer->read_stamp + event->time_delta;
+			ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
+							 cpu_buffer->cpu, ts);
+		}
+		if (lost_events)
+			*lost_events = rb_lost_events(cpu_buffer);
+		return event;
+
+	default:
+		RB_WARN_ON(cpu_buffer, 1);
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_peek);
+
+static struct ring_buffer_event *
+rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
+{
+	struct trace_buffer *buffer;
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_event *event;
+	int nr_loops = 0;
+
+	if (ts)
+		*ts = 0;
+
+	cpu_buffer = iter->cpu_buffer;
+	buffer = cpu_buffer->buffer;
+
+	/*
+	 * Check if someone performed a consuming read to the buffer
+	 * or removed some pages from the buffer. In these cases,
+	 * iterator was invalidated and we need to reset it.
+	 */
+	if (unlikely(iter->cache_read != cpu_buffer->read ||
+		     iter->cache_reader_page != cpu_buffer->reader_page ||
+		     iter->cache_pages_removed != cpu_buffer->pages_removed))
+		rb_iter_reset(iter);
+
+ again:
+	if (ring_buffer_iter_empty(iter))
+		return NULL;
+
+	/*
+	 * As the writer can mess with what the iterator is trying
+	 * to read, just give up if we fail to get an event after
+	 * three tries. The iterator is not as reliable when reading
+	 * the ring buffer with an active write as the consumer is.
+	 * Do not warn if the three failures is reached.
+	 */
+	if (++nr_loops > 3)
+		return NULL;
+
+	if (rb_per_cpu_empty(cpu_buffer))
+		return NULL;
+
+	if (iter->head >= rb_page_size(iter->head_page)) {
+		rb_inc_iter(iter);
+		goto again;
+	}
+
+	event = rb_iter_head_event(iter);
+	if (!event)
+		goto again;
+
+	switch (event->type_len) {
+	case RINGBUF_TYPE_PADDING:
+		if (rb_null_event(event)) {
+			rb_inc_iter(iter);
+			goto again;
+		}
+		rb_advance_iter(iter);
+		return event;
+
+	case RINGBUF_TYPE_TIME_EXTEND:
+		/* Internal data, OK to advance */
+		rb_advance_iter(iter);
+		goto again;
+
+	case RINGBUF_TYPE_TIME_STAMP:
+		if (ts) {
+			*ts = rb_event_time_stamp(event);
+			*ts = rb_fix_abs_ts(*ts, iter->head_page->page->time_stamp);
+			ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
+							 cpu_buffer->cpu, ts);
+		}
+		/* Internal data, OK to advance */
+		rb_advance_iter(iter);
+		goto again;
+
+	case RINGBUF_TYPE_DATA:
+		if (ts && !(*ts)) {
+			*ts = iter->read_stamp + event->time_delta;
+			ring_buffer_normalize_time_stamp(buffer,
+							 cpu_buffer->cpu, ts);
+		}
+		return event;
+
+	default:
+		RB_WARN_ON(cpu_buffer, 1);
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
+
+static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	if (likely(!in_nmi())) {
+		raw_spin_lock(&cpu_buffer->reader_lock);
+		return true;
+	}
+
+	/*
+	 * If an NMI die dumps out the content of the ring buffer
+	 * trylock must be used to prevent a deadlock if the NMI
+	 * preempted a task that holds the ring buffer locks. If
+	 * we get the lock then all is fine, if not, then continue
+	 * to do the read, but this can corrupt the ring buffer,
+	 * so it must be permanently disabled from future writes.
+	 * Reading from NMI is a oneshot deal.
+	 */
+	if (raw_spin_trylock(&cpu_buffer->reader_lock))
+		return true;
+
+	/* Continue without locking, but disable the ring buffer */
+	atomic_inc(&cpu_buffer->record_disabled);
+	return false;
+}
+
+static inline void
+rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
+{
+	if (likely(locked))
+		raw_spin_unlock(&cpu_buffer->reader_lock);
+}
+
+/**
+ * ring_buffer_peek - peek at the next event to be read
+ * @buffer: The ring buffer to read
+ * @cpu: The cpu to peak at
+ * @ts: The timestamp counter of this event.
+ * @lost_events: a variable to store if events were lost (may be NULL)
+ *
+ * This will return the event that will be read next, but does
+ * not consume the data.
+ */
+struct ring_buffer_event *
+ring_buffer_peek(struct trace_buffer *buffer, int cpu, u64 *ts,
+		 unsigned long *lost_events)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+	struct ring_buffer_event *event;
+	unsigned long flags;
+	bool dolock;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return NULL;
+
+ again:
+	local_irq_save(flags);
+	dolock = rb_reader_lock(cpu_buffer);
+	event = rb_buffer_peek(cpu_buffer, ts, lost_events);
+	if (event && event->type_len == RINGBUF_TYPE_PADDING)
+		rb_advance_reader(cpu_buffer);
+	rb_reader_unlock(cpu_buffer, dolock);
+	local_irq_restore(flags);
+
+	if (event && event->type_len == RINGBUF_TYPE_PADDING)
+		goto again;
+
+	return event;
+}
+
+/** ring_buffer_iter_dropped - report if there are dropped events
+ * @iter: The ring buffer iterator
+ *
+ * Returns true if there was dropped events since the last peek.
+ */
+bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter)
+{
+	bool ret = iter->missed_events != 0;
+
+	iter->missed_events = 0;
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_iter_dropped);
+
+/**
+ * ring_buffer_iter_peek - peek at the next event to be read
+ * @iter: The ring buffer iterator
+ * @ts: The timestamp counter of this event.
+ *
+ * This will return the event that will be read next, but does
+ * not increment the iterator.
+ */
+struct ring_buffer_event *
+ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+	struct ring_buffer_event *event;
+	unsigned long flags;
+
+ again:
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	event = rb_iter_peek(iter, ts);
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+	if (event && event->type_len == RINGBUF_TYPE_PADDING)
+		goto again;
+
+	return event;
+}
+
+/**
+ * ring_buffer_consume - return an event and consume it
+ * @buffer: The ring buffer to get the next event from
+ * @cpu: the cpu to read the buffer from
+ * @ts: a variable to store the timestamp (may be NULL)
+ * @lost_events: a variable to store if events were lost (may be NULL)
+ *
+ * Returns the next event in the ring buffer, and that event is consumed.
+ * Meaning, that sequential reads will keep returning a different event,
+ * and eventually empty the ring buffer if the producer is slower.
+ */
+struct ring_buffer_event *
+ring_buffer_consume(struct trace_buffer *buffer, int cpu, u64 *ts,
+		    unsigned long *lost_events)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_event *event = NULL;
+	unsigned long flags;
+	bool dolock;
+
+ again:
+	/* might be called in atomic */
+	preempt_disable();
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		goto out;
+
+	cpu_buffer = buffer->buffers[cpu];
+	local_irq_save(flags);
+	dolock = rb_reader_lock(cpu_buffer);
+
+	event = rb_buffer_peek(cpu_buffer, ts, lost_events);
+	if (event) {
+		cpu_buffer->lost_events = 0;
+		rb_advance_reader(cpu_buffer);
+	}
+
+	rb_reader_unlock(cpu_buffer, dolock);
+	local_irq_restore(flags);
+
+ out:
+	preempt_enable();
+
+	if (event && event->type_len == RINGBUF_TYPE_PADDING)
+		goto again;
+
+	return event;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_consume);
+
+/**
+ * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
+ * @buffer: The ring buffer to read from
+ * @cpu: The cpu buffer to iterate over
+ * @flags: gfp flags to use for memory allocation
+ *
+ * This performs the initial preparations necessary to iterate
+ * through the buffer.  Memory is allocated, buffer recording
+ * is disabled, and the iterator pointer is returned to the caller.
+ *
+ * Disabling buffer recording prevents the reading from being
+ * corrupted. This is not a consuming read, so a producer is not
+ * expected.
+ *
+ * After a sequence of ring_buffer_read_prepare calls, the user is
+ * expected to make at least one call to ring_buffer_read_prepare_sync.
+ * Afterwards, ring_buffer_read_start is invoked to get things going
+ * for real.
+ *
+ * This overall must be paired with ring_buffer_read_finish.
+ */
+struct ring_buffer_iter *
+ring_buffer_read_prepare(struct trace_buffer *buffer, int cpu, gfp_t flags)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_iter *iter;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return NULL;
+
+	iter = kzalloc(sizeof(*iter), flags);
+	if (!iter)
+		return NULL;
+
+	/* Holds the entire event: data and meta data */
+	iter->event = kmalloc(BUF_PAGE_SIZE, flags);
+	if (!iter->event) {
+		kfree(iter);
+		return NULL;
+	}
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	iter->cpu_buffer = cpu_buffer;
+
+	atomic_inc(&cpu_buffer->resize_disabled);
+
+	return iter;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
+
+/**
+ * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
+ *
+ * All previously invoked ring_buffer_read_prepare calls to prepare
+ * iterators will be synchronized.  Afterwards, read_buffer_read_start
+ * calls on those iterators are allowed.
+ */
+void
+ring_buffer_read_prepare_sync(void)
+{
+	synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
+
+/**
+ * ring_buffer_read_start - start a non consuming read of the buffer
+ * @iter: The iterator returned by ring_buffer_read_prepare
+ *
+ * This finalizes the startup of an iteration through the buffer.
+ * The iterator comes from a call to ring_buffer_read_prepare and
+ * an intervening ring_buffer_read_prepare_sync must have been
+ * performed.
+ *
+ * Must be paired with ring_buffer_read_finish.
+ */
+void
+ring_buffer_read_start(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags;
+
+	if (!iter)
+		return;
+
+	cpu_buffer = iter->cpu_buffer;
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	arch_spin_lock(&cpu_buffer->lock);
+	rb_iter_reset(iter);
+	arch_spin_unlock(&cpu_buffer->lock);
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_start);
+
+/**
+ * ring_buffer_read_finish - finish reading the iterator of the buffer
+ * @iter: The iterator retrieved by ring_buffer_start
+ *
+ * This re-enables the recording to the buffer, and frees the
+ * iterator.
+ */
+void
+ring_buffer_read_finish(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+	unsigned long flags;
+
+	/*
+	 * Ring buffer is disabled from recording, here's a good place
+	 * to check the integrity of the ring buffer.
+	 * Must prevent readers from trying to read, as the check
+	 * clears the HEAD page and readers require it.
+	 */
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	rb_check_pages(cpu_buffer);
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+	atomic_dec(&cpu_buffer->resize_disabled);
+	kfree(iter->event);
+	kfree(iter);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
+
+/**
+ * ring_buffer_iter_advance - advance the iterator to the next location
+ * @iter: The ring buffer iterator
+ *
+ * Move the location of the iterator such that the next read will
+ * be the next location of the iterator.
+ */
+void ring_buffer_iter_advance(struct ring_buffer_iter *iter)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	rb_advance_iter(iter);
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_iter_advance);
+
+/**
+ * ring_buffer_size - return the size of the ring buffer (in bytes)
+ * @buffer: The ring buffer.
+ * @cpu: The CPU to get ring buffer size from.
+ */
+unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu)
+{
+	/*
+	 * Earlier, this method returned
+	 *	BUF_PAGE_SIZE * buffer->nr_pages
+	 * Since the nr_pages field is now removed, we have converted this to
+	 * return the per cpu buffer value.
+	 */
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_size);
+
+static void rb_clear_buffer_page(struct buffer_page *page)
+{
+	local_set(&page->write, 0);
+	local_set(&page->entries, 0);
+	rb_init_page(page->page);
+	page->read = 0;
+}
+
+static void
+rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct buffer_page *page;
+
+	rb_head_page_deactivate(cpu_buffer);
+
+	cpu_buffer->head_page
+		= list_entry(cpu_buffer->pages, struct buffer_page, list);
+	rb_clear_buffer_page(cpu_buffer->head_page);
+	list_for_each_entry(page, cpu_buffer->pages, list) {
+		rb_clear_buffer_page(page);
+	}
+
+	cpu_buffer->tail_page = cpu_buffer->head_page;
+	cpu_buffer->commit_page = cpu_buffer->head_page;
+
+	INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
+	INIT_LIST_HEAD(&cpu_buffer->new_pages);
+	rb_clear_buffer_page(cpu_buffer->reader_page);
+
+	local_set(&cpu_buffer->entries_bytes, 0);
+	local_set(&cpu_buffer->overrun, 0);
+	local_set(&cpu_buffer->commit_overrun, 0);
+	local_set(&cpu_buffer->dropped_events, 0);
+	local_set(&cpu_buffer->entries, 0);
+	local_set(&cpu_buffer->committing, 0);
+	local_set(&cpu_buffer->commits, 0);
+	local_set(&cpu_buffer->pages_touched, 0);
+	local_set(&cpu_buffer->pages_lost, 0);
+	local_set(&cpu_buffer->pages_read, 0);
+	cpu_buffer->last_pages_touch = 0;
+	cpu_buffer->shortest_full = 0;
+	cpu_buffer->read = 0;
+	cpu_buffer->read_bytes = 0;
+
+	rb_time_set(&cpu_buffer->write_stamp, 0);
+	rb_time_set(&cpu_buffer->before_stamp, 0);
+
+	memset(cpu_buffer->event_stamp, 0, sizeof(cpu_buffer->event_stamp));
+
+	cpu_buffer->lost_events = 0;
+	cpu_buffer->last_overrun = 0;
+
+	rb_head_page_activate(cpu_buffer);
+	cpu_buffer->pages_removed = 0;
+}
+
+/* Must have disabled the cpu buffer then done a synchronize_rcu */
+static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
+		goto out;
+
+	arch_spin_lock(&cpu_buffer->lock);
+
+	rb_reset_cpu(cpu_buffer);
+
+	arch_spin_unlock(&cpu_buffer->lock);
+
+ out:
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+}
+
+/**
+ * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
+ * @buffer: The ring buffer to reset a per cpu buffer of
+ * @cpu: The CPU buffer to be reset
+ */
+void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return;
+
+	/* prevent another thread from changing buffer sizes */
+	mutex_lock(&buffer->mutex);
+
+	atomic_inc(&cpu_buffer->resize_disabled);
+	atomic_inc(&cpu_buffer->record_disabled);
+
+	/* Make sure all commits have finished */
+	synchronize_rcu();
+
+	reset_disabled_cpu_buffer(cpu_buffer);
+
+	atomic_dec(&cpu_buffer->record_disabled);
+	atomic_dec(&cpu_buffer->resize_disabled);
+
+	mutex_unlock(&buffer->mutex);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
+
+/* Flag to ensure proper resetting of atomic variables */
+#define RESET_BIT	(1 << 30)
+
+/**
+ * ring_buffer_reset_online_cpus - reset a ring buffer per CPU buffer
+ * @buffer: The ring buffer to reset a per cpu buffer of
+ */
+void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	int cpu;
+
+	/* prevent another thread from changing buffer sizes */
+	mutex_lock(&buffer->mutex);
+
+	for_each_online_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		atomic_add(RESET_BIT, &cpu_buffer->resize_disabled);
+		atomic_inc(&cpu_buffer->record_disabled);
+	}
+
+	/* Make sure all commits have finished */
+	synchronize_rcu();
+
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		/*
+		 * If a CPU came online during the synchronize_rcu(), then
+		 * ignore it.
+		 */
+		if (!(atomic_read(&cpu_buffer->resize_disabled) & RESET_BIT))
+			continue;
+
+		reset_disabled_cpu_buffer(cpu_buffer);
+
+		atomic_dec(&cpu_buffer->record_disabled);
+		atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled);
+	}
+
+	mutex_unlock(&buffer->mutex);
+}
+
+/**
+ * ring_buffer_reset - reset a ring buffer
+ * @buffer: The ring buffer to reset all cpu buffers
+ */
+void ring_buffer_reset(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	int cpu;
+
+	/* prevent another thread from changing buffer sizes */
+	mutex_lock(&buffer->mutex);
+
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		atomic_inc(&cpu_buffer->resize_disabled);
+		atomic_inc(&cpu_buffer->record_disabled);
+	}
+
+	/* Make sure all commits have finished */
+	synchronize_rcu();
+
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+
+		reset_disabled_cpu_buffer(cpu_buffer);
+
+		atomic_dec(&cpu_buffer->record_disabled);
+		atomic_dec(&cpu_buffer->resize_disabled);
+	}
+
+	mutex_unlock(&buffer->mutex);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_reset);
+
+/**
+ * ring_buffer_empty - is the ring buffer empty?
+ * @buffer: The ring buffer to test
+ */
+bool ring_buffer_empty(struct trace_buffer *buffer)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags;
+	bool dolock;
+	bool ret;
+	int cpu;
+
+	/* yes this is racy, but if you don't like the race, lock the buffer */
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+		local_irq_save(flags);
+		dolock = rb_reader_lock(cpu_buffer);
+		ret = rb_per_cpu_empty(cpu_buffer);
+		rb_reader_unlock(cpu_buffer, dolock);
+		local_irq_restore(flags);
+
+		if (!ret)
+			return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_empty);
+
+/**
+ * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
+ * @buffer: The ring buffer
+ * @cpu: The CPU buffer to test
+ */
+bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags;
+	bool dolock;
+	bool ret;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return true;
+
+	cpu_buffer = buffer->buffers[cpu];
+	local_irq_save(flags);
+	dolock = rb_reader_lock(cpu_buffer);
+	ret = rb_per_cpu_empty(cpu_buffer);
+	rb_reader_unlock(cpu_buffer, dolock);
+	local_irq_restore(flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
+
+#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
+/**
+ * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
+ * @buffer_a: One buffer to swap with
+ * @buffer_b: The other buffer to swap with
+ * @cpu: the CPU of the buffers to swap
+ *
+ * This function is useful for tracers that want to take a "snapshot"
+ * of a CPU buffer and has another back up buffer lying around.
+ * it is expected that the tracer handles the cpu buffer not being
+ * used at the moment.
+ */
+int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
+			 struct trace_buffer *buffer_b, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer_a;
+	struct ring_buffer_per_cpu *cpu_buffer_b;
+	int ret = -EINVAL;
+
+	if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
+	    !cpumask_test_cpu(cpu, buffer_b->cpumask))
+		goto out;
+
+	cpu_buffer_a = buffer_a->buffers[cpu];
+	cpu_buffer_b = buffer_b->buffers[cpu];
+
+	/* At least make sure the two buffers are somewhat the same */
+	if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
+		goto out;
+
+	ret = -EAGAIN;
+
+	if (atomic_read(&buffer_a->record_disabled))
+		goto out;
+
+	if (atomic_read(&buffer_b->record_disabled))
+		goto out;
+
+	if (atomic_read(&cpu_buffer_a->record_disabled))
+		goto out;
+
+	if (atomic_read(&cpu_buffer_b->record_disabled))
+		goto out;
+
+	/*
+	 * We can't do a synchronize_rcu here because this
+	 * function can be called in atomic context.
+	 * Normally this will be called from the same CPU as cpu.
+	 * If not it's up to the caller to protect this.
+	 */
+	atomic_inc(&cpu_buffer_a->record_disabled);
+	atomic_inc(&cpu_buffer_b->record_disabled);
+
+	ret = -EBUSY;
+	if (local_read(&cpu_buffer_a->committing))
+		goto out_dec;
+	if (local_read(&cpu_buffer_b->committing))
+		goto out_dec;
+
+	/*
+	 * When resize is in progress, we cannot swap it because
+	 * it will mess the state of the cpu buffer.
+	 */
+	if (atomic_read(&buffer_a->resizing))
+		goto out_dec;
+	if (atomic_read(&buffer_b->resizing))
+		goto out_dec;
+
+	buffer_a->buffers[cpu] = cpu_buffer_b;
+	buffer_b->buffers[cpu] = cpu_buffer_a;
+
+	cpu_buffer_b->buffer = buffer_a;
+	cpu_buffer_a->buffer = buffer_b;
+
+	ret = 0;
+
+out_dec:
+	atomic_dec(&cpu_buffer_a->record_disabled);
+	atomic_dec(&cpu_buffer_b->record_disabled);
+out:
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
+#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
+
+/**
+ * ring_buffer_alloc_read_page - allocate a page to read from buffer
+ * @buffer: the buffer to allocate for.
+ * @cpu: the cpu buffer to allocate.
+ *
+ * This function is used in conjunction with ring_buffer_read_page.
+ * When reading a full page from the ring buffer, these functions
+ * can be used to speed up the process. The calling function should
+ * allocate a few pages first with this function. Then when it
+ * needs to get pages from the ring buffer, it passes the result
+ * of this function into ring_buffer_read_page, which will swap
+ * the page that was allocated, with the read page of the buffer.
+ *
+ * Returns:
+ *  The page allocated, or ERR_PTR
+ */
+void *ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct buffer_data_page *bpage = NULL;
+	unsigned long flags;
+	struct page *page;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return ERR_PTR(-ENODEV);
+
+	cpu_buffer = buffer->buffers[cpu];
+	local_irq_save(flags);
+	arch_spin_lock(&cpu_buffer->lock);
+
+	if (cpu_buffer->free_page) {
+		bpage = cpu_buffer->free_page;
+		cpu_buffer->free_page = NULL;
+	}
+
+	arch_spin_unlock(&cpu_buffer->lock);
+	local_irq_restore(flags);
+
+	if (bpage)
+		goto out;
+
+	page = alloc_pages_node(cpu_to_node(cpu),
+				GFP_KERNEL | __GFP_NORETRY, 0);
+	if (!page)
+		return ERR_PTR(-ENOMEM);
+
+	bpage = page_address(page);
+
+ out:
+	rb_init_page(bpage);
+
+	return bpage;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
+
+/**
+ * ring_buffer_free_read_page - free an allocated read page
+ * @buffer: the buffer the page was allocate for
+ * @cpu: the cpu buffer the page came from
+ * @data: the page to free
+ *
+ * Free a page allocated from ring_buffer_alloc_read_page.
+ */
+void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu, void *data)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct buffer_data_page *bpage = data;
+	struct page *page = virt_to_page(bpage);
+	unsigned long flags;
+
+	if (!buffer || !buffer->buffers || !buffer->buffers[cpu])
+		return;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	/* If the page is still in use someplace else, we can't reuse it */
+	if (page_ref_count(page) > 1)
+		goto out;
+
+	local_irq_save(flags);
+	arch_spin_lock(&cpu_buffer->lock);
+
+	if (!cpu_buffer->free_page) {
+		cpu_buffer->free_page = bpage;
+		bpage = NULL;
+	}
+
+	arch_spin_unlock(&cpu_buffer->lock);
+	local_irq_restore(flags);
+
+ out:
+	free_page((unsigned long)bpage);
+}
+EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
+
+/**
+ * ring_buffer_read_page - extract a page from the ring buffer
+ * @buffer: buffer to extract from
+ * @data_page: the page to use allocated from ring_buffer_alloc_read_page
+ * @len: amount to extract
+ * @cpu: the cpu of the buffer to extract
+ * @full: should the extraction only happen when the page is full.
+ *
+ * This function will pull out a page from the ring buffer and consume it.
+ * @data_page must be the address of the variable that was returned
+ * from ring_buffer_alloc_read_page. This is because the page might be used
+ * to swap with a page in the ring buffer.
+ *
+ * for example:
+ *	rpage = ring_buffer_alloc_read_page(buffer, cpu);
+ *	if (IS_ERR(rpage))
+ *		return PTR_ERR(rpage);
+ *	ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
+ *	if (ret >= 0)
+ *		process_page(rpage, ret);
+ *
+ * When @full is set, the function will not return true unless
+ * the writer is off the reader page.
+ *
+ * Note: it is up to the calling functions to handle sleeps and wakeups.
+ *  The ring buffer can be used anywhere in the kernel and can not
+ *  blindly call wake_up. The layer that uses the ring buffer must be
+ *  responsible for that.
+ *
+ * Returns:
+ *  >=0 if data has been transferred, returns the offset of consumed data.
+ *  <0 if no data has been transferred.
+ */
+int ring_buffer_read_page(struct trace_buffer *buffer,
+			  void **data_page, size_t len, int cpu, int full)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+	struct ring_buffer_event *event;
+	struct buffer_data_page *bpage;
+	struct buffer_page *reader;
+	unsigned long missed_events;
+	unsigned long flags;
+	unsigned int commit;
+	unsigned int read;
+	u64 save_timestamp;
+	int ret = -1;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		goto out;
+
+	/*
+	 * If len is not big enough to hold the page header, then
+	 * we can not copy anything.
+	 */
+	if (len <= BUF_PAGE_HDR_SIZE)
+		goto out;
+
+	len -= BUF_PAGE_HDR_SIZE;
+
+	if (!data_page)
+		goto out;
+
+	bpage = *data_page;
+	if (!bpage)
+		goto out;
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	reader = rb_get_reader_page(cpu_buffer);
+	if (!reader)
+		goto out_unlock;
+
+	event = rb_reader_event(cpu_buffer);
+
+	read = reader->read;
+	commit = rb_page_commit(reader);
+
+	/* Check if any events were dropped */
+	missed_events = cpu_buffer->lost_events;
+
+	/*
+	 * If this page has been partially read or
+	 * if len is not big enough to read the rest of the page or
+	 * a writer is still on the page, then
+	 * we must copy the data from the page to the buffer.
+	 * Otherwise, we can simply swap the page with the one passed in.
+	 */
+	if (read || (len < (commit - read)) ||
+	    cpu_buffer->reader_page == cpu_buffer->commit_page) {
+		struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
+		unsigned int rpos = read;
+		unsigned int pos = 0;
+		unsigned int size;
+
+		/*
+		 * If a full page is expected, this can still be returned
+		 * if there's been a previous partial read and the
+		 * rest of the page can be read and the commit page is off
+		 * the reader page.
+		 */
+		if (full &&
+		    (!read || (len < (commit - read)) ||
+		     cpu_buffer->reader_page == cpu_buffer->commit_page))
+			goto out_unlock;
+
+		if (len > (commit - read))
+			len = (commit - read);
+
+		/* Always keep the time extend and data together */
+		size = rb_event_ts_length(event);
+
+		if (len < size)
+			goto out_unlock;
+
+		/* save the current timestamp, since the user will need it */
+		save_timestamp = cpu_buffer->read_stamp;
+
+		/* Need to copy one event at a time */
+		do {
+			/* We need the size of one event, because
+			 * rb_advance_reader only advances by one event,
+			 * whereas rb_event_ts_length may include the size of
+			 * one or two events.
+			 * We have already ensured there's enough space if this
+			 * is a time extend. */
+			size = rb_event_length(event);
+			memcpy(bpage->data + pos, rpage->data + rpos, size);
+
+			len -= size;
+
+			rb_advance_reader(cpu_buffer);
+			rpos = reader->read;
+			pos += size;
+
+			if (rpos >= commit)
+				break;
+
+			event = rb_reader_event(cpu_buffer);
+			/* Always keep the time extend and data together */
+			size = rb_event_ts_length(event);
+		} while (len >= size);
+
+		/* update bpage */
+		local_set(&bpage->commit, pos);
+		bpage->time_stamp = save_timestamp;
+
+		/* we copied everything to the beginning */
+		read = 0;
+	} else {
+		/* update the entry counter */
+		cpu_buffer->read += rb_page_entries(reader);
+		cpu_buffer->read_bytes += rb_page_commit(reader);
+
+		/* swap the pages */
+		rb_init_page(bpage);
+		bpage = reader->page;
+		reader->page = *data_page;
+		local_set(&reader->write, 0);
+		local_set(&reader->entries, 0);
+		reader->read = 0;
+		*data_page = bpage;
+
+		/*
+		 * Use the real_end for the data size,
+		 * This gives us a chance to store the lost events
+		 * on the page.
+		 */
+		if (reader->real_end)
+			local_set(&bpage->commit, reader->real_end);
+	}
+	ret = read;
+
+	cpu_buffer->lost_events = 0;
+
+	commit = local_read(&bpage->commit);
+	/*
+	 * Set a flag in the commit field if we lost events
+	 */
+	if (missed_events) {
+		/* If there is room at the end of the page to save the
+		 * missed events, then record it there.
+		 */
+		if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
+			memcpy(&bpage->data[commit], &missed_events,
+			       sizeof(missed_events));
+			local_add(RB_MISSED_STORED, &bpage->commit);
+			commit += sizeof(missed_events);
+		}
+		local_add(RB_MISSED_EVENTS, &bpage->commit);
+	}
+
+	/*
+	 * This page may be off to user land. Zero it out here.
+	 */
+	if (commit < BUF_PAGE_SIZE)
+		memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
+
+ out_unlock:
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+ out:
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_page);
+
+/*
+ * We only allocate new buffers, never free them if the CPU goes down.
+ * If we were to free the buffer, then the user would lose any trace that was in
+ * the buffer.
+ */
+int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node)
+{
+	struct trace_buffer *buffer;
+	long nr_pages_same;
+	int cpu_i;
+	unsigned long nr_pages;
+
+	buffer = container_of(node, struct trace_buffer, node);
+	if (cpumask_test_cpu(cpu, buffer->cpumask))
+		return 0;
+
+	nr_pages = 0;
+	nr_pages_same = 1;
+	/* check if all cpu sizes are same */
+	for_each_buffer_cpu(buffer, cpu_i) {
+		/* fill in the size from first enabled cpu */
+		if (nr_pages == 0)
+			nr_pages = buffer->buffers[cpu_i]->nr_pages;
+		if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
+			nr_pages_same = 0;
+			break;
+		}
+	}
+	/* allocate minimum pages, user can later expand it */
+	if (!nr_pages_same)
+		nr_pages = 2;
+	buffer->buffers[cpu] =
+		rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
+	if (!buffer->buffers[cpu]) {
+		WARN(1, "failed to allocate ring buffer on CPU %u\n",
+		     cpu);
+		return -ENOMEM;
+	}
+	smp_wmb();
+	cpumask_set_cpu(cpu, buffer->cpumask);
+	return 0;
+}
+
+#ifdef CONFIG_RING_BUFFER_STARTUP_TEST
+/*
+ * This is a basic integrity check of the ring buffer.
+ * Late in the boot cycle this test will run when configured in.
+ * It will kick off a thread per CPU that will go into a loop
+ * writing to the per cpu ring buffer various sizes of data.
+ * Some of the data will be large items, some small.
+ *
+ * Another thread is created that goes into a spin, sending out
+ * IPIs to the other CPUs to also write into the ring buffer.
+ * this is to test the nesting ability of the buffer.
+ *
+ * Basic stats are recorded and reported. If something in the
+ * ring buffer should happen that's not expected, a big warning
+ * is displayed and all ring buffers are disabled.
+ */
+static struct task_struct *rb_threads[NR_CPUS] __initdata;
+
+struct rb_test_data {
+	struct trace_buffer *buffer;
+	unsigned long		events;
+	unsigned long		bytes_written;
+	unsigned long		bytes_alloc;
+	unsigned long		bytes_dropped;
+	unsigned long		events_nested;
+	unsigned long		bytes_written_nested;
+	unsigned long		bytes_alloc_nested;
+	unsigned long		bytes_dropped_nested;
+	int			min_size_nested;
+	int			max_size_nested;
+	int			max_size;
+	int			min_size;
+	int			cpu;
+	int			cnt;
+};
+
+static struct rb_test_data rb_data[NR_CPUS] __initdata;
+
+/* 1 meg per cpu */
+#define RB_TEST_BUFFER_SIZE	1048576
+
+static char rb_string[] __initdata =
+	"abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
+	"?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
+	"!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
+
+static bool rb_test_started __initdata;
+
+struct rb_item {
+	int size;
+	char str[];
+};
+
+static __init int rb_write_something(struct rb_test_data *data, bool nested)
+{
+	struct ring_buffer_event *event;
+	struct rb_item *item;
+	bool started;
+	int event_len;
+	int size;
+	int len;
+	int cnt;
+
+	/* Have nested writes different that what is written */
+	cnt = data->cnt + (nested ? 27 : 0);
+
+	/* Multiply cnt by ~e, to make some unique increment */
+	size = (cnt * 68 / 25) % (sizeof(rb_string) - 1);
+
+	len = size + sizeof(struct rb_item);
+
+	started = rb_test_started;
+	/* read rb_test_started before checking buffer enabled */
+	smp_rmb();
+
+	event = ring_buffer_lock_reserve(data->buffer, len);
+	if (!event) {
+		/* Ignore dropped events before test starts. */
+		if (started) {
+			if (nested)
+				data->bytes_dropped += len;
+			else
+				data->bytes_dropped_nested += len;
+		}
+		return len;
+	}
+
+	event_len = ring_buffer_event_length(event);
+
+	if (RB_WARN_ON(data->buffer, event_len < len))
+		goto out;
+
+	item = ring_buffer_event_data(event);
+	item->size = size;
+	memcpy(item->str, rb_string, size);
+
+	if (nested) {
+		data->bytes_alloc_nested += event_len;
+		data->bytes_written_nested += len;
+		data->events_nested++;
+		if (!data->min_size_nested || len < data->min_size_nested)
+			data->min_size_nested = len;
+		if (len > data->max_size_nested)
+			data->max_size_nested = len;
+	} else {
+		data->bytes_alloc += event_len;
+		data->bytes_written += len;
+		data->events++;
+		if (!data->min_size || len < data->min_size)
+			data->max_size = len;
+		if (len > data->max_size)
+			data->max_size = len;
+	}
+
+ out:
+	ring_buffer_unlock_commit(data->buffer);
+
+	return 0;
+}
+
+static __init int rb_test(void *arg)
+{
+	struct rb_test_data *data = arg;
+
+	while (!kthread_should_stop()) {
+		rb_write_something(data, false);
+		data->cnt++;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		/* Now sleep between a min of 100-300us and a max of 1ms */
+		usleep_range(((data->cnt % 3) + 1) * 100, 1000);
+	}
+
+	return 0;
+}
+
+static __init void rb_ipi(void *ignore)
+{
+	struct rb_test_data *data;
+	int cpu = smp_processor_id();
+
+	data = &rb_data[cpu];
+	rb_write_something(data, true);
+}
+
+static __init int rb_hammer_test(void *arg)
+{
+	while (!kthread_should_stop()) {
+
+		/* Send an IPI to all cpus to write data! */
+		smp_call_function(rb_ipi, NULL, 1);
+		/* No sleep, but for non preempt, let others run */
+		schedule();
+	}
+
+	return 0;
+}
+
+static __init int test_ringbuffer(void)
+{
+	struct task_struct *rb_hammer;
+	struct trace_buffer *buffer;
+	int cpu;
+	int ret = 0;
+
+	if (security_locked_down(LOCKDOWN_TRACEFS)) {
+		pr_warn("Lockdown is enabled, skipping ring buffer tests\n");
+		return 0;
+	}
+
+	pr_info("Running ring buffer tests...\n");
+
+	buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
+	if (WARN_ON(!buffer))
+		return 0;
+
+	/* Disable buffer so that threads can't write to it yet */
+	ring_buffer_record_off(buffer);
+
+	for_each_online_cpu(cpu) {
+		rb_data[cpu].buffer = buffer;
+		rb_data[cpu].cpu = cpu;
+		rb_data[cpu].cnt = cpu;
+		rb_threads[cpu] = kthread_run_on_cpu(rb_test, &rb_data[cpu],
+						     cpu, "rbtester/%u");
+		if (WARN_ON(IS_ERR(rb_threads[cpu]))) {
+			pr_cont("FAILED\n");
+			ret = PTR_ERR(rb_threads[cpu]);
+			goto out_free;
+		}
+	}
+
+	/* Now create the rb hammer! */
+	rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
+	if (WARN_ON(IS_ERR(rb_hammer))) {
+		pr_cont("FAILED\n");
+		ret = PTR_ERR(rb_hammer);
+		goto out_free;
+	}
+
+	ring_buffer_record_on(buffer);
+	/*
+	 * Show buffer is enabled before setting rb_test_started.
+	 * Yes there's a small race window where events could be
+	 * dropped and the thread wont catch it. But when a ring
+	 * buffer gets enabled, there will always be some kind of
+	 * delay before other CPUs see it. Thus, we don't care about
+	 * those dropped events. We care about events dropped after
+	 * the threads see that the buffer is active.
+	 */
+	smp_wmb();
+	rb_test_started = true;
+
+	set_current_state(TASK_INTERRUPTIBLE);
+	/* Just run for 10 seconds */;
+	schedule_timeout(10 * HZ);
+
+	kthread_stop(rb_hammer);
+
+ out_free:
+	for_each_online_cpu(cpu) {
+		if (!rb_threads[cpu])
+			break;
+		kthread_stop(rb_threads[cpu]);
+	}
+	if (ret) {
+		ring_buffer_free(buffer);
+		return ret;
+	}
+
+	/* Report! */
+	pr_info("finished\n");
+	for_each_online_cpu(cpu) {
+		struct ring_buffer_event *event;
+		struct rb_test_data *data = &rb_data[cpu];
+		struct rb_item *item;
+		unsigned long total_events;
+		unsigned long total_dropped;
+		unsigned long total_written;
+		unsigned long total_alloc;
+		unsigned long total_read = 0;
+		unsigned long total_size = 0;
+		unsigned long total_len = 0;
+		unsigned long total_lost = 0;
+		unsigned long lost;
+		int big_event_size;
+		int small_event_size;
+
+		ret = -1;
+
+		total_events = data->events + data->events_nested;
+		total_written = data->bytes_written + data->bytes_written_nested;
+		total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
+		total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
+
+		big_event_size = data->max_size + data->max_size_nested;
+		small_event_size = data->min_size + data->min_size_nested;
+
+		pr_info("CPU %d:\n", cpu);
+		pr_info("              events:    %ld\n", total_events);
+		pr_info("       dropped bytes:    %ld\n", total_dropped);
+		pr_info("       alloced bytes:    %ld\n", total_alloc);
+		pr_info("       written bytes:    %ld\n", total_written);
+		pr_info("       biggest event:    %d\n", big_event_size);
+		pr_info("      smallest event:    %d\n", small_event_size);
+
+		if (RB_WARN_ON(buffer, total_dropped))
+			break;
+
+		ret = 0;
+
+		while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
+			total_lost += lost;
+			item = ring_buffer_event_data(event);
+			total_len += ring_buffer_event_length(event);
+			total_size += item->size + sizeof(struct rb_item);
+			if (memcmp(&item->str[0], rb_string, item->size) != 0) {
+				pr_info("FAILED!\n");
+				pr_info("buffer had: %.*s\n", item->size, item->str);
+				pr_info("expected:   %.*s\n", item->size, rb_string);
+				RB_WARN_ON(buffer, 1);
+				ret = -1;
+				break;
+			}
+			total_read++;
+		}
+		if (ret)
+			break;
+
+		ret = -1;
+
+		pr_info("         read events:   %ld\n", total_read);
+		pr_info("         lost events:   %ld\n", total_lost);
+		pr_info("        total events:   %ld\n", total_lost + total_read);
+		pr_info("  recorded len bytes:   %ld\n", total_len);
+		pr_info(" recorded size bytes:   %ld\n", total_size);
+		if (total_lost) {
+			pr_info(" With dropped events, record len and size may not match\n"
+				" alloced and written from above\n");
+		} else {
+			if (RB_WARN_ON(buffer, total_len != total_alloc ||
+				       total_size != total_written))
+				break;
+		}
+		if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
+			break;
+
+		ret = 0;
+	}
+	if (!ret)
+		pr_info("Ring buffer PASSED!\n");
+
+	ring_buffer_free(buffer);
+	return 0;
+}
+
+late_initcall(test_ringbuffer);
+#endif /* CONFIG_RING_BUFFER_STARTUP_TEST */