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-rw-r--r--kernel/printk/printk.c3975
1 files changed, 3975 insertions, 0 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
new file mode 100644
index 000000000..cc53fb77f
--- /dev/null
+++ b/kernel/printk/printk.c
@@ -0,0 +1,3975 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/kernel/printk.c
+ *
+ * Copyright (C) 1991, 1992 Linus Torvalds
+ *
+ * Modified to make sys_syslog() more flexible: added commands to
+ * return the last 4k of kernel messages, regardless of whether
+ * they've been read or not. Added option to suppress kernel printk's
+ * to the console. Added hook for sending the console messages
+ * elsewhere, in preparation for a serial line console (someday).
+ * Ted Ts'o, 2/11/93.
+ * Modified for sysctl support, 1/8/97, Chris Horn.
+ * Fixed SMP synchronization, 08/08/99, Manfred Spraul
+ * manfred@colorfullife.com
+ * Rewrote bits to get rid of console_lock
+ * 01Mar01 Andrew Morton
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/jiffies.h>
+#include <linux/nmi.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/delay.h>
+#include <linux/smp.h>
+#include <linux/security.h>
+#include <linux/memblock.h>
+#include <linux/syscalls.h>
+#include <linux/crash_core.h>
+#include <linux/ratelimit.h>
+#include <linux/kmsg_dump.h>
+#include <linux/syslog.h>
+#include <linux/cpu.h>
+#include <linux/rculist.h>
+#include <linux/poll.h>
+#include <linux/irq_work.h>
+#include <linux/ctype.h>
+#include <linux/uio.h>
+#include <linux/sched/clock.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/task_stack.h>
+
+#include <linux/uaccess.h>
+#include <asm/sections.h>
+
+#include <trace/events/initcall.h>
+#define CREATE_TRACE_POINTS
+#include <trace/events/printk.h>
+
+#include "printk_ringbuffer.h"
+#include "console_cmdline.h"
+#include "braille.h"
+#include "internal.h"
+
+int console_printk[4] = {
+ CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
+ MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
+ CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
+ CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
+};
+EXPORT_SYMBOL_GPL(console_printk);
+
+atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
+EXPORT_SYMBOL(ignore_console_lock_warning);
+
+/*
+ * Low level drivers may need that to know if they can schedule in
+ * their unblank() callback or not. So let's export it.
+ */
+int oops_in_progress;
+EXPORT_SYMBOL(oops_in_progress);
+
+/*
+ * console_sem protects the console_drivers list, and also
+ * provides serialisation for access to the entire console
+ * driver system.
+ */
+static DEFINE_SEMAPHORE(console_sem);
+struct console *console_drivers;
+EXPORT_SYMBOL_GPL(console_drivers);
+
+/*
+ * System may need to suppress printk message under certain
+ * circumstances, like after kernel panic happens.
+ */
+int __read_mostly suppress_printk;
+
+/*
+ * During panic, heavy printk by other CPUs can delay the
+ * panic and risk deadlock on console resources.
+ */
+static int __read_mostly suppress_panic_printk;
+
+#ifdef CONFIG_LOCKDEP
+static struct lockdep_map console_lock_dep_map = {
+ .name = "console_lock"
+};
+#endif
+
+enum devkmsg_log_bits {
+ __DEVKMSG_LOG_BIT_ON = 0,
+ __DEVKMSG_LOG_BIT_OFF,
+ __DEVKMSG_LOG_BIT_LOCK,
+};
+
+enum devkmsg_log_masks {
+ DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
+ DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
+ DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
+};
+
+/* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
+#define DEVKMSG_LOG_MASK_DEFAULT 0
+
+static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
+
+static int __control_devkmsg(char *str)
+{
+ size_t len;
+
+ if (!str)
+ return -EINVAL;
+
+ len = str_has_prefix(str, "on");
+ if (len) {
+ devkmsg_log = DEVKMSG_LOG_MASK_ON;
+ return len;
+ }
+
+ len = str_has_prefix(str, "off");
+ if (len) {
+ devkmsg_log = DEVKMSG_LOG_MASK_OFF;
+ return len;
+ }
+
+ len = str_has_prefix(str, "ratelimit");
+ if (len) {
+ devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
+ return len;
+ }
+
+ return -EINVAL;
+}
+
+static int __init control_devkmsg(char *str)
+{
+ if (__control_devkmsg(str) < 0) {
+ pr_warn("printk.devkmsg: bad option string '%s'\n", str);
+ return 1;
+ }
+
+ /*
+ * Set sysctl string accordingly:
+ */
+ if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
+ strcpy(devkmsg_log_str, "on");
+ else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
+ strcpy(devkmsg_log_str, "off");
+ /* else "ratelimit" which is set by default. */
+
+ /*
+ * Sysctl cannot change it anymore. The kernel command line setting of
+ * this parameter is to force the setting to be permanent throughout the
+ * runtime of the system. This is a precation measure against userspace
+ * trying to be a smarta** and attempting to change it up on us.
+ */
+ devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
+
+ return 1;
+}
+__setup("printk.devkmsg=", control_devkmsg);
+
+char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
+#if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
+int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ char old_str[DEVKMSG_STR_MAX_SIZE];
+ unsigned int old;
+ int err;
+
+ if (write) {
+ if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
+ return -EINVAL;
+
+ old = devkmsg_log;
+ strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
+ }
+
+ err = proc_dostring(table, write, buffer, lenp, ppos);
+ if (err)
+ return err;
+
+ if (write) {
+ err = __control_devkmsg(devkmsg_log_str);
+
+ /*
+ * Do not accept an unknown string OR a known string with
+ * trailing crap...
+ */
+ if (err < 0 || (err + 1 != *lenp)) {
+
+ /* ... and restore old setting. */
+ devkmsg_log = old;
+ strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
+
+ return -EINVAL;
+ }
+ }
+
+ return 0;
+}
+#endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
+
+/*
+ * Helper macros to handle lockdep when locking/unlocking console_sem. We use
+ * macros instead of functions so that _RET_IP_ contains useful information.
+ */
+#define down_console_sem() do { \
+ down(&console_sem);\
+ mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
+} while (0)
+
+static int __down_trylock_console_sem(unsigned long ip)
+{
+ int lock_failed;
+ unsigned long flags;
+
+ /*
+ * Here and in __up_console_sem() we need to be in safe mode,
+ * because spindump/WARN/etc from under console ->lock will
+ * deadlock in printk()->down_trylock_console_sem() otherwise.
+ */
+ printk_safe_enter_irqsave(flags);
+ lock_failed = down_trylock(&console_sem);
+ printk_safe_exit_irqrestore(flags);
+
+ if (lock_failed)
+ return 1;
+ mutex_acquire(&console_lock_dep_map, 0, 1, ip);
+ return 0;
+}
+#define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
+
+static void __up_console_sem(unsigned long ip)
+{
+ unsigned long flags;
+
+ mutex_release(&console_lock_dep_map, ip);
+
+ printk_safe_enter_irqsave(flags);
+ up(&console_sem);
+ printk_safe_exit_irqrestore(flags);
+}
+#define up_console_sem() __up_console_sem(_RET_IP_)
+
+static bool panic_in_progress(void)
+{
+ return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
+}
+
+/*
+ * This is used for debugging the mess that is the VT code by
+ * keeping track if we have the console semaphore held. It's
+ * definitely not the perfect debug tool (we don't know if _WE_
+ * hold it and are racing, but it helps tracking those weird code
+ * paths in the console code where we end up in places I want
+ * locked without the console semaphore held).
+ */
+static int console_locked, console_suspended;
+
+/*
+ * Array of consoles built from command line options (console=)
+ */
+
+#define MAX_CMDLINECONSOLES 8
+
+static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
+
+static int preferred_console = -1;
+int console_set_on_cmdline;
+EXPORT_SYMBOL(console_set_on_cmdline);
+
+/* Flag: console code may call schedule() */
+static int console_may_schedule;
+
+enum con_msg_format_flags {
+ MSG_FORMAT_DEFAULT = 0,
+ MSG_FORMAT_SYSLOG = (1 << 0),
+};
+
+static int console_msg_format = MSG_FORMAT_DEFAULT;
+
+/*
+ * The printk log buffer consists of a sequenced collection of records, each
+ * containing variable length message text. Every record also contains its
+ * own meta-data (@info).
+ *
+ * Every record meta-data carries the timestamp in microseconds, as well as
+ * the standard userspace syslog level and syslog facility. The usual kernel
+ * messages use LOG_KERN; userspace-injected messages always carry a matching
+ * syslog facility, by default LOG_USER. The origin of every message can be
+ * reliably determined that way.
+ *
+ * The human readable log message of a record is available in @text, the
+ * length of the message text in @text_len. The stored message is not
+ * terminated.
+ *
+ * Optionally, a record can carry a dictionary of properties (key/value
+ * pairs), to provide userspace with a machine-readable message context.
+ *
+ * Examples for well-defined, commonly used property names are:
+ * DEVICE=b12:8 device identifier
+ * b12:8 block dev_t
+ * c127:3 char dev_t
+ * n8 netdev ifindex
+ * +sound:card0 subsystem:devname
+ * SUBSYSTEM=pci driver-core subsystem name
+ *
+ * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
+ * and values are terminated by a '\0' character.
+ *
+ * Example of record values:
+ * record.text_buf = "it's a line" (unterminated)
+ * record.info.seq = 56
+ * record.info.ts_nsec = 36863
+ * record.info.text_len = 11
+ * record.info.facility = 0 (LOG_KERN)
+ * record.info.flags = 0
+ * record.info.level = 3 (LOG_ERR)
+ * record.info.caller_id = 299 (task 299)
+ * record.info.dev_info.subsystem = "pci" (terminated)
+ * record.info.dev_info.device = "+pci:0000:00:01.0" (terminated)
+ *
+ * The 'struct printk_info' buffer must never be directly exported to
+ * userspace, it is a kernel-private implementation detail that might
+ * need to be changed in the future, when the requirements change.
+ *
+ * /dev/kmsg exports the structured data in the following line format:
+ * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
+ *
+ * Users of the export format should ignore possible additional values
+ * separated by ',', and find the message after the ';' character.
+ *
+ * The optional key/value pairs are attached as continuation lines starting
+ * with a space character and terminated by a newline. All possible
+ * non-prinatable characters are escaped in the "\xff" notation.
+ */
+
+/* syslog_lock protects syslog_* variables and write access to clear_seq. */
+static DEFINE_MUTEX(syslog_lock);
+
+#ifdef CONFIG_PRINTK
+DECLARE_WAIT_QUEUE_HEAD(log_wait);
+/* All 3 protected by @syslog_lock. */
+/* the next printk record to read by syslog(READ) or /proc/kmsg */
+static u64 syslog_seq;
+static size_t syslog_partial;
+static bool syslog_time;
+
+struct latched_seq {
+ seqcount_latch_t latch;
+ u64 val[2];
+};
+
+/*
+ * The next printk record to read after the last 'clear' command. There are
+ * two copies (updated with seqcount_latch) so that reads can locklessly
+ * access a valid value. Writers are synchronized by @syslog_lock.
+ */
+static struct latched_seq clear_seq = {
+ .latch = SEQCNT_LATCH_ZERO(clear_seq.latch),
+ .val[0] = 0,
+ .val[1] = 0,
+};
+
+#ifdef CONFIG_PRINTK_CALLER
+#define PREFIX_MAX 48
+#else
+#define PREFIX_MAX 32
+#endif
+
+/* the maximum size of a formatted record (i.e. with prefix added per line) */
+#define CONSOLE_LOG_MAX 1024
+
+/* the maximum size for a dropped text message */
+#define DROPPED_TEXT_MAX 64
+
+/* the maximum size allowed to be reserved for a record */
+#define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX)
+
+#define LOG_LEVEL(v) ((v) & 0x07)
+#define LOG_FACILITY(v) ((v) >> 3 & 0xff)
+
+/* record buffer */
+#define LOG_ALIGN __alignof__(unsigned long)
+#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
+#define LOG_BUF_LEN_MAX (u32)(1 << 31)
+static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
+static char *log_buf = __log_buf;
+static u32 log_buf_len = __LOG_BUF_LEN;
+
+/*
+ * Define the average message size. This only affects the number of
+ * descriptors that will be available. Underestimating is better than
+ * overestimating (too many available descriptors is better than not enough).
+ */
+#define PRB_AVGBITS 5 /* 32 character average length */
+
+#if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
+#error CONFIG_LOG_BUF_SHIFT value too small.
+#endif
+_DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
+ PRB_AVGBITS, &__log_buf[0]);
+
+static struct printk_ringbuffer printk_rb_dynamic;
+
+static struct printk_ringbuffer *prb = &printk_rb_static;
+
+/*
+ * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
+ * per_cpu_areas are initialised. This variable is set to true when
+ * it's safe to access per-CPU data.
+ */
+static bool __printk_percpu_data_ready __ro_after_init;
+
+bool printk_percpu_data_ready(void)
+{
+ return __printk_percpu_data_ready;
+}
+
+/* Must be called under syslog_lock. */
+static void latched_seq_write(struct latched_seq *ls, u64 val)
+{
+ raw_write_seqcount_latch(&ls->latch);
+ ls->val[0] = val;
+ raw_write_seqcount_latch(&ls->latch);
+ ls->val[1] = val;
+}
+
+/* Can be called from any context. */
+static u64 latched_seq_read_nolock(struct latched_seq *ls)
+{
+ unsigned int seq;
+ unsigned int idx;
+ u64 val;
+
+ do {
+ seq = raw_read_seqcount_latch(&ls->latch);
+ idx = seq & 0x1;
+ val = ls->val[idx];
+ } while (read_seqcount_latch_retry(&ls->latch, seq));
+
+ return val;
+}
+
+/* Return log buffer address */
+char *log_buf_addr_get(void)
+{
+ return log_buf;
+}
+
+/* Return log buffer size */
+u32 log_buf_len_get(void)
+{
+ return log_buf_len;
+}
+
+/*
+ * Define how much of the log buffer we could take at maximum. The value
+ * must be greater than two. Note that only half of the buffer is available
+ * when the index points to the middle.
+ */
+#define MAX_LOG_TAKE_PART 4
+static const char trunc_msg[] = "<truncated>";
+
+static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
+{
+ /*
+ * The message should not take the whole buffer. Otherwise, it might
+ * get removed too soon.
+ */
+ u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
+
+ if (*text_len > max_text_len)
+ *text_len = max_text_len;
+
+ /* enable the warning message (if there is room) */
+ *trunc_msg_len = strlen(trunc_msg);
+ if (*text_len >= *trunc_msg_len)
+ *text_len -= *trunc_msg_len;
+ else
+ *trunc_msg_len = 0;
+}
+
+int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
+
+static int syslog_action_restricted(int type)
+{
+ if (dmesg_restrict)
+ return 1;
+ /*
+ * Unless restricted, we allow "read all" and "get buffer size"
+ * for everybody.
+ */
+ return type != SYSLOG_ACTION_READ_ALL &&
+ type != SYSLOG_ACTION_SIZE_BUFFER;
+}
+
+static int check_syslog_permissions(int type, int source)
+{
+ /*
+ * If this is from /proc/kmsg and we've already opened it, then we've
+ * already done the capabilities checks at open time.
+ */
+ if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
+ goto ok;
+
+ if (syslog_action_restricted(type)) {
+ if (capable(CAP_SYSLOG))
+ goto ok;
+ /*
+ * For historical reasons, accept CAP_SYS_ADMIN too, with
+ * a warning.
+ */
+ if (capable(CAP_SYS_ADMIN)) {
+ pr_warn_once("%s (%d): Attempt to access syslog with "
+ "CAP_SYS_ADMIN but no CAP_SYSLOG "
+ "(deprecated).\n",
+ current->comm, task_pid_nr(current));
+ goto ok;
+ }
+ return -EPERM;
+ }
+ok:
+ return security_syslog(type);
+}
+
+static void append_char(char **pp, char *e, char c)
+{
+ if (*pp < e)
+ *(*pp)++ = c;
+}
+
+static ssize_t info_print_ext_header(char *buf, size_t size,
+ struct printk_info *info)
+{
+ u64 ts_usec = info->ts_nsec;
+ char caller[20];
+#ifdef CONFIG_PRINTK_CALLER
+ u32 id = info->caller_id;
+
+ snprintf(caller, sizeof(caller), ",caller=%c%u",
+ id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+#else
+ caller[0] = '\0';
+#endif
+
+ do_div(ts_usec, 1000);
+
+ return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
+ (info->facility << 3) | info->level, info->seq,
+ ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
+}
+
+static ssize_t msg_add_ext_text(char *buf, size_t size,
+ const char *text, size_t text_len,
+ unsigned char endc)
+{
+ char *p = buf, *e = buf + size;
+ size_t i;
+
+ /* escape non-printable characters */
+ for (i = 0; i < text_len; i++) {
+ unsigned char c = text[i];
+
+ if (c < ' ' || c >= 127 || c == '\\')
+ p += scnprintf(p, e - p, "\\x%02x", c);
+ else
+ append_char(&p, e, c);
+ }
+ append_char(&p, e, endc);
+
+ return p - buf;
+}
+
+static ssize_t msg_add_dict_text(char *buf, size_t size,
+ const char *key, const char *val)
+{
+ size_t val_len = strlen(val);
+ ssize_t len;
+
+ if (!val_len)
+ return 0;
+
+ len = msg_add_ext_text(buf, size, "", 0, ' '); /* dict prefix */
+ len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
+ len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
+
+ return len;
+}
+
+static ssize_t msg_print_ext_body(char *buf, size_t size,
+ char *text, size_t text_len,
+ struct dev_printk_info *dev_info)
+{
+ ssize_t len;
+
+ len = msg_add_ext_text(buf, size, text, text_len, '\n');
+
+ if (!dev_info)
+ goto out;
+
+ len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
+ dev_info->subsystem);
+ len += msg_add_dict_text(buf + len, size - len, "DEVICE",
+ dev_info->device);
+out:
+ return len;
+}
+
+/* /dev/kmsg - userspace message inject/listen interface */
+struct devkmsg_user {
+ atomic64_t seq;
+ struct ratelimit_state rs;
+ struct mutex lock;
+ char buf[CONSOLE_EXT_LOG_MAX];
+
+ struct printk_info info;
+ char text_buf[CONSOLE_EXT_LOG_MAX];
+ struct printk_record record;
+};
+
+static __printf(3, 4) __cold
+int devkmsg_emit(int facility, int level, const char *fmt, ...)
+{
+ va_list args;
+ int r;
+
+ va_start(args, fmt);
+ r = vprintk_emit(facility, level, NULL, fmt, args);
+ va_end(args);
+
+ return r;
+}
+
+static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
+{
+ char *buf, *line;
+ int level = default_message_loglevel;
+ int facility = 1; /* LOG_USER */
+ struct file *file = iocb->ki_filp;
+ struct devkmsg_user *user = file->private_data;
+ size_t len = iov_iter_count(from);
+ ssize_t ret = len;
+
+ if (!user || len > LOG_LINE_MAX)
+ return -EINVAL;
+
+ /* Ignore when user logging is disabled. */
+ if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
+ return len;
+
+ /* Ratelimit when not explicitly enabled. */
+ if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
+ if (!___ratelimit(&user->rs, current->comm))
+ return ret;
+ }
+
+ buf = kmalloc(len+1, GFP_KERNEL);
+ if (buf == NULL)
+ return -ENOMEM;
+
+ buf[len] = '\0';
+ if (!copy_from_iter_full(buf, len, from)) {
+ kfree(buf);
+ return -EFAULT;
+ }
+
+ /*
+ * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
+ * the decimal value represents 32bit, the lower 3 bit are the log
+ * level, the rest are the log facility.
+ *
+ * If no prefix or no userspace facility is specified, we
+ * enforce LOG_USER, to be able to reliably distinguish
+ * kernel-generated messages from userspace-injected ones.
+ */
+ line = buf;
+ if (line[0] == '<') {
+ char *endp = NULL;
+ unsigned int u;
+
+ u = simple_strtoul(line + 1, &endp, 10);
+ if (endp && endp[0] == '>') {
+ level = LOG_LEVEL(u);
+ if (LOG_FACILITY(u) != 0)
+ facility = LOG_FACILITY(u);
+ endp++;
+ line = endp;
+ }
+ }
+
+ devkmsg_emit(facility, level, "%s", line);
+ kfree(buf);
+ return ret;
+}
+
+static ssize_t devkmsg_read(struct file *file, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct devkmsg_user *user = file->private_data;
+ struct printk_record *r = &user->record;
+ size_t len;
+ ssize_t ret;
+
+ if (!user)
+ return -EBADF;
+
+ ret = mutex_lock_interruptible(&user->lock);
+ if (ret)
+ return ret;
+
+ if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
+ if (file->f_flags & O_NONBLOCK) {
+ ret = -EAGAIN;
+ goto out;
+ }
+
+ /*
+ * Guarantee this task is visible on the waitqueue before
+ * checking the wake condition.
+ *
+ * The full memory barrier within set_current_state() of
+ * prepare_to_wait_event() pairs with the full memory barrier
+ * within wq_has_sleeper().
+ *
+ * This pairs with __wake_up_klogd:A.
+ */
+ ret = wait_event_interruptible(log_wait,
+ prb_read_valid(prb,
+ atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
+ if (ret)
+ goto out;
+ }
+
+ if (r->info->seq != atomic64_read(&user->seq)) {
+ /* our last seen message is gone, return error and reset */
+ atomic64_set(&user->seq, r->info->seq);
+ ret = -EPIPE;
+ goto out;
+ }
+
+ len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
+ len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
+ &r->text_buf[0], r->info->text_len,
+ &r->info->dev_info);
+
+ atomic64_set(&user->seq, r->info->seq + 1);
+
+ if (len > count) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ if (copy_to_user(buf, user->buf, len)) {
+ ret = -EFAULT;
+ goto out;
+ }
+ ret = len;
+out:
+ mutex_unlock(&user->lock);
+ return ret;
+}
+
+/*
+ * Be careful when modifying this function!!!
+ *
+ * Only few operations are supported because the device works only with the
+ * entire variable length messages (records). Non-standard values are
+ * returned in the other cases and has been this way for quite some time.
+ * User space applications might depend on this behavior.
+ */
+static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
+{
+ struct devkmsg_user *user = file->private_data;
+ loff_t ret = 0;
+
+ if (!user)
+ return -EBADF;
+ if (offset)
+ return -ESPIPE;
+
+ switch (whence) {
+ case SEEK_SET:
+ /* the first record */
+ atomic64_set(&user->seq, prb_first_valid_seq(prb));
+ break;
+ case SEEK_DATA:
+ /*
+ * The first record after the last SYSLOG_ACTION_CLEAR,
+ * like issued by 'dmesg -c'. Reading /dev/kmsg itself
+ * changes no global state, and does not clear anything.
+ */
+ atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
+ break;
+ case SEEK_END:
+ /* after the last record */
+ atomic64_set(&user->seq, prb_next_seq(prb));
+ break;
+ default:
+ ret = -EINVAL;
+ }
+ return ret;
+}
+
+static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
+{
+ struct devkmsg_user *user = file->private_data;
+ struct printk_info info;
+ __poll_t ret = 0;
+
+ if (!user)
+ return EPOLLERR|EPOLLNVAL;
+
+ poll_wait(file, &log_wait, wait);
+
+ if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
+ /* return error when data has vanished underneath us */
+ if (info.seq != atomic64_read(&user->seq))
+ ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
+ else
+ ret = EPOLLIN|EPOLLRDNORM;
+ }
+
+ return ret;
+}
+
+static int devkmsg_open(struct inode *inode, struct file *file)
+{
+ struct devkmsg_user *user;
+ int err;
+
+ if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
+ return -EPERM;
+
+ /* write-only does not need any file context */
+ if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
+ err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+ SYSLOG_FROM_READER);
+ if (err)
+ return err;
+ }
+
+ user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
+ if (!user)
+ return -ENOMEM;
+
+ ratelimit_default_init(&user->rs);
+ ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
+
+ mutex_init(&user->lock);
+
+ prb_rec_init_rd(&user->record, &user->info,
+ &user->text_buf[0], sizeof(user->text_buf));
+
+ atomic64_set(&user->seq, prb_first_valid_seq(prb));
+
+ file->private_data = user;
+ return 0;
+}
+
+static int devkmsg_release(struct inode *inode, struct file *file)
+{
+ struct devkmsg_user *user = file->private_data;
+
+ if (!user)
+ return 0;
+
+ ratelimit_state_exit(&user->rs);
+
+ mutex_destroy(&user->lock);
+ kvfree(user);
+ return 0;
+}
+
+const struct file_operations kmsg_fops = {
+ .open = devkmsg_open,
+ .read = devkmsg_read,
+ .write_iter = devkmsg_write,
+ .llseek = devkmsg_llseek,
+ .poll = devkmsg_poll,
+ .release = devkmsg_release,
+};
+
+#ifdef CONFIG_CRASH_CORE
+/*
+ * This appends the listed symbols to /proc/vmcore
+ *
+ * /proc/vmcore is used by various utilities, like crash and makedumpfile to
+ * obtain access to symbols that are otherwise very difficult to locate. These
+ * symbols are specifically used so that utilities can access and extract the
+ * dmesg log from a vmcore file after a crash.
+ */
+void log_buf_vmcoreinfo_setup(void)
+{
+ struct dev_printk_info *dev_info = NULL;
+
+ VMCOREINFO_SYMBOL(prb);
+ VMCOREINFO_SYMBOL(printk_rb_static);
+ VMCOREINFO_SYMBOL(clear_seq);
+
+ /*
+ * Export struct size and field offsets. User space tools can
+ * parse it and detect any changes to structure down the line.
+ */
+
+ VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
+ VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
+ VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
+ VMCOREINFO_OFFSET(printk_ringbuffer, fail);
+
+ VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
+ VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
+ VMCOREINFO_OFFSET(prb_desc_ring, descs);
+ VMCOREINFO_OFFSET(prb_desc_ring, infos);
+ VMCOREINFO_OFFSET(prb_desc_ring, head_id);
+ VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
+
+ VMCOREINFO_STRUCT_SIZE(prb_desc);
+ VMCOREINFO_OFFSET(prb_desc, state_var);
+ VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
+
+ VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
+ VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
+ VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
+
+ VMCOREINFO_STRUCT_SIZE(printk_info);
+ VMCOREINFO_OFFSET(printk_info, seq);
+ VMCOREINFO_OFFSET(printk_info, ts_nsec);
+ VMCOREINFO_OFFSET(printk_info, text_len);
+ VMCOREINFO_OFFSET(printk_info, caller_id);
+ VMCOREINFO_OFFSET(printk_info, dev_info);
+
+ VMCOREINFO_STRUCT_SIZE(dev_printk_info);
+ VMCOREINFO_OFFSET(dev_printk_info, subsystem);
+ VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
+ VMCOREINFO_OFFSET(dev_printk_info, device);
+ VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
+
+ VMCOREINFO_STRUCT_SIZE(prb_data_ring);
+ VMCOREINFO_OFFSET(prb_data_ring, size_bits);
+ VMCOREINFO_OFFSET(prb_data_ring, data);
+ VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
+ VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
+
+ VMCOREINFO_SIZE(atomic_long_t);
+ VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
+
+ VMCOREINFO_STRUCT_SIZE(latched_seq);
+ VMCOREINFO_OFFSET(latched_seq, val);
+}
+#endif
+
+/* requested log_buf_len from kernel cmdline */
+static unsigned long __initdata new_log_buf_len;
+
+/* we practice scaling the ring buffer by powers of 2 */
+static void __init log_buf_len_update(u64 size)
+{
+ if (size > (u64)LOG_BUF_LEN_MAX) {
+ size = (u64)LOG_BUF_LEN_MAX;
+ pr_err("log_buf over 2G is not supported.\n");
+ }
+
+ if (size)
+ size = roundup_pow_of_two(size);
+ if (size > log_buf_len)
+ new_log_buf_len = (unsigned long)size;
+}
+
+/* save requested log_buf_len since it's too early to process it */
+static int __init log_buf_len_setup(char *str)
+{
+ u64 size;
+
+ if (!str)
+ return -EINVAL;
+
+ size = memparse(str, &str);
+
+ log_buf_len_update(size);
+
+ return 0;
+}
+early_param("log_buf_len", log_buf_len_setup);
+
+#ifdef CONFIG_SMP
+#define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
+
+static void __init log_buf_add_cpu(void)
+{
+ unsigned int cpu_extra;
+
+ /*
+ * archs should set up cpu_possible_bits properly with
+ * set_cpu_possible() after setup_arch() but just in
+ * case lets ensure this is valid.
+ */
+ if (num_possible_cpus() == 1)
+ return;
+
+ cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
+
+ /* by default this will only continue through for large > 64 CPUs */
+ if (cpu_extra <= __LOG_BUF_LEN / 2)
+ return;
+
+ pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
+ __LOG_CPU_MAX_BUF_LEN);
+ pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
+ cpu_extra);
+ pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
+
+ log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
+}
+#else /* !CONFIG_SMP */
+static inline void log_buf_add_cpu(void) {}
+#endif /* CONFIG_SMP */
+
+static void __init set_percpu_data_ready(void)
+{
+ __printk_percpu_data_ready = true;
+}
+
+static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
+ struct printk_record *r)
+{
+ struct prb_reserved_entry e;
+ struct printk_record dest_r;
+
+ prb_rec_init_wr(&dest_r, r->info->text_len);
+
+ if (!prb_reserve(&e, rb, &dest_r))
+ return 0;
+
+ memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
+ dest_r.info->text_len = r->info->text_len;
+ dest_r.info->facility = r->info->facility;
+ dest_r.info->level = r->info->level;
+ dest_r.info->flags = r->info->flags;
+ dest_r.info->ts_nsec = r->info->ts_nsec;
+ dest_r.info->caller_id = r->info->caller_id;
+ memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
+
+ prb_final_commit(&e);
+
+ return prb_record_text_space(&e);
+}
+
+static char setup_text_buf[LOG_LINE_MAX] __initdata;
+
+void __init setup_log_buf(int early)
+{
+ struct printk_info *new_infos;
+ unsigned int new_descs_count;
+ struct prb_desc *new_descs;
+ struct printk_info info;
+ struct printk_record r;
+ unsigned int text_size;
+ size_t new_descs_size;
+ size_t new_infos_size;
+ unsigned long flags;
+ char *new_log_buf;
+ unsigned int free;
+ u64 seq;
+
+ /*
+ * Some archs call setup_log_buf() multiple times - first is very
+ * early, e.g. from setup_arch(), and second - when percpu_areas
+ * are initialised.
+ */
+ if (!early)
+ set_percpu_data_ready();
+
+ if (log_buf != __log_buf)
+ return;
+
+ if (!early && !new_log_buf_len)
+ log_buf_add_cpu();
+
+ if (!new_log_buf_len)
+ return;
+
+ new_descs_count = new_log_buf_len >> PRB_AVGBITS;
+ if (new_descs_count == 0) {
+ pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
+ return;
+ }
+
+ new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
+ if (unlikely(!new_log_buf)) {
+ pr_err("log_buf_len: %lu text bytes not available\n",
+ new_log_buf_len);
+ return;
+ }
+
+ new_descs_size = new_descs_count * sizeof(struct prb_desc);
+ new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
+ if (unlikely(!new_descs)) {
+ pr_err("log_buf_len: %zu desc bytes not available\n",
+ new_descs_size);
+ goto err_free_log_buf;
+ }
+
+ new_infos_size = new_descs_count * sizeof(struct printk_info);
+ new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
+ if (unlikely(!new_infos)) {
+ pr_err("log_buf_len: %zu info bytes not available\n",
+ new_infos_size);
+ goto err_free_descs;
+ }
+
+ prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
+
+ prb_init(&printk_rb_dynamic,
+ new_log_buf, ilog2(new_log_buf_len),
+ new_descs, ilog2(new_descs_count),
+ new_infos);
+
+ local_irq_save(flags);
+
+ log_buf_len = new_log_buf_len;
+ log_buf = new_log_buf;
+ new_log_buf_len = 0;
+
+ free = __LOG_BUF_LEN;
+ prb_for_each_record(0, &printk_rb_static, seq, &r) {
+ text_size = add_to_rb(&printk_rb_dynamic, &r);
+ if (text_size > free)
+ free = 0;
+ else
+ free -= text_size;
+ }
+
+ prb = &printk_rb_dynamic;
+
+ local_irq_restore(flags);
+
+ /*
+ * Copy any remaining messages that might have appeared from
+ * NMI context after copying but before switching to the
+ * dynamic buffer.
+ */
+ prb_for_each_record(seq, &printk_rb_static, seq, &r) {
+ text_size = add_to_rb(&printk_rb_dynamic, &r);
+ if (text_size > free)
+ free = 0;
+ else
+ free -= text_size;
+ }
+
+ if (seq != prb_next_seq(&printk_rb_static)) {
+ pr_err("dropped %llu messages\n",
+ prb_next_seq(&printk_rb_static) - seq);
+ }
+
+ pr_info("log_buf_len: %u bytes\n", log_buf_len);
+ pr_info("early log buf free: %u(%u%%)\n",
+ free, (free * 100) / __LOG_BUF_LEN);
+ return;
+
+err_free_descs:
+ memblock_free(new_descs, new_descs_size);
+err_free_log_buf:
+ memblock_free(new_log_buf, new_log_buf_len);
+}
+
+static bool __read_mostly ignore_loglevel;
+
+static int __init ignore_loglevel_setup(char *str)
+{
+ ignore_loglevel = true;
+ pr_info("debug: ignoring loglevel setting.\n");
+
+ return 0;
+}
+
+early_param("ignore_loglevel", ignore_loglevel_setup);
+module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(ignore_loglevel,
+ "ignore loglevel setting (prints all kernel messages to the console)");
+
+static bool suppress_message_printing(int level)
+{
+ return (level >= console_loglevel && !ignore_loglevel);
+}
+
+#ifdef CONFIG_BOOT_PRINTK_DELAY
+
+static int boot_delay; /* msecs delay after each printk during bootup */
+static unsigned long long loops_per_msec; /* based on boot_delay */
+
+static int __init boot_delay_setup(char *str)
+{
+ unsigned long lpj;
+
+ lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
+ loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
+
+ get_option(&str, &boot_delay);
+ if (boot_delay > 10 * 1000)
+ boot_delay = 0;
+
+ pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
+ "HZ: %d, loops_per_msec: %llu\n",
+ boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
+ return 0;
+}
+early_param("boot_delay", boot_delay_setup);
+
+static void boot_delay_msec(int level)
+{
+ unsigned long long k;
+ unsigned long timeout;
+
+ if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
+ || suppress_message_printing(level)) {
+ return;
+ }
+
+ k = (unsigned long long)loops_per_msec * boot_delay;
+
+ timeout = jiffies + msecs_to_jiffies(boot_delay);
+ while (k) {
+ k--;
+ cpu_relax();
+ /*
+ * use (volatile) jiffies to prevent
+ * compiler reduction; loop termination via jiffies
+ * is secondary and may or may not happen.
+ */
+ if (time_after(jiffies, timeout))
+ break;
+ touch_nmi_watchdog();
+ }
+}
+#else
+static inline void boot_delay_msec(int level)
+{
+}
+#endif
+
+static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
+module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
+
+static size_t print_syslog(unsigned int level, char *buf)
+{
+ return sprintf(buf, "<%u>", level);
+}
+
+static size_t print_time(u64 ts, char *buf)
+{
+ unsigned long rem_nsec = do_div(ts, 1000000000);
+
+ return sprintf(buf, "[%5lu.%06lu]",
+ (unsigned long)ts, rem_nsec / 1000);
+}
+
+#ifdef CONFIG_PRINTK_CALLER
+static size_t print_caller(u32 id, char *buf)
+{
+ char caller[12];
+
+ snprintf(caller, sizeof(caller), "%c%u",
+ id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
+ return sprintf(buf, "[%6s]", caller);
+}
+#else
+#define print_caller(id, buf) 0
+#endif
+
+static size_t info_print_prefix(const struct printk_info *info, bool syslog,
+ bool time, char *buf)
+{
+ size_t len = 0;
+
+ if (syslog)
+ len = print_syslog((info->facility << 3) | info->level, buf);
+
+ if (time)
+ len += print_time(info->ts_nsec, buf + len);
+
+ len += print_caller(info->caller_id, buf + len);
+
+ if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
+ buf[len++] = ' ';
+ buf[len] = '\0';
+ }
+
+ return len;
+}
+
+/*
+ * Prepare the record for printing. The text is shifted within the given
+ * buffer to avoid a need for another one. The following operations are
+ * done:
+ *
+ * - Add prefix for each line.
+ * - Drop truncated lines that no longer fit into the buffer.
+ * - Add the trailing newline that has been removed in vprintk_store().
+ * - Add a string terminator.
+ *
+ * Since the produced string is always terminated, the maximum possible
+ * return value is @r->text_buf_size - 1;
+ *
+ * Return: The length of the updated/prepared text, including the added
+ * prefixes and the newline. The terminator is not counted. The dropped
+ * line(s) are not counted.
+ */
+static size_t record_print_text(struct printk_record *r, bool syslog,
+ bool time)
+{
+ size_t text_len = r->info->text_len;
+ size_t buf_size = r->text_buf_size;
+ char *text = r->text_buf;
+ char prefix[PREFIX_MAX];
+ bool truncated = false;
+ size_t prefix_len;
+ size_t line_len;
+ size_t len = 0;
+ char *next;
+
+ /*
+ * If the message was truncated because the buffer was not large
+ * enough, treat the available text as if it were the full text.
+ */
+ if (text_len > buf_size)
+ text_len = buf_size;
+
+ prefix_len = info_print_prefix(r->info, syslog, time, prefix);
+
+ /*
+ * @text_len: bytes of unprocessed text
+ * @line_len: bytes of current line _without_ newline
+ * @text: pointer to beginning of current line
+ * @len: number of bytes prepared in r->text_buf
+ */
+ for (;;) {
+ next = memchr(text, '\n', text_len);
+ if (next) {
+ line_len = next - text;
+ } else {
+ /* Drop truncated line(s). */
+ if (truncated)
+ break;
+ line_len = text_len;
+ }
+
+ /*
+ * Truncate the text if there is not enough space to add the
+ * prefix and a trailing newline and a terminator.
+ */
+ if (len + prefix_len + text_len + 1 + 1 > buf_size) {
+ /* Drop even the current line if no space. */
+ if (len + prefix_len + line_len + 1 + 1 > buf_size)
+ break;
+
+ text_len = buf_size - len - prefix_len - 1 - 1;
+ truncated = true;
+ }
+
+ memmove(text + prefix_len, text, text_len);
+ memcpy(text, prefix, prefix_len);
+
+ /*
+ * Increment the prepared length to include the text and
+ * prefix that were just moved+copied. Also increment for the
+ * newline at the end of this line. If this is the last line,
+ * there is no newline, but it will be added immediately below.
+ */
+ len += prefix_len + line_len + 1;
+ if (text_len == line_len) {
+ /*
+ * This is the last line. Add the trailing newline
+ * removed in vprintk_store().
+ */
+ text[prefix_len + line_len] = '\n';
+ break;
+ }
+
+ /*
+ * Advance beyond the added prefix and the related line with
+ * its newline.
+ */
+ text += prefix_len + line_len + 1;
+
+ /*
+ * The remaining text has only decreased by the line with its
+ * newline.
+ *
+ * Note that @text_len can become zero. It happens when @text
+ * ended with a newline (either due to truncation or the
+ * original string ending with "\n\n"). The loop is correctly
+ * repeated and (if not truncated) an empty line with a prefix
+ * will be prepared.
+ */
+ text_len -= line_len + 1;
+ }
+
+ /*
+ * If a buffer was provided, it will be terminated. Space for the
+ * string terminator is guaranteed to be available. The terminator is
+ * not counted in the return value.
+ */
+ if (buf_size > 0)
+ r->text_buf[len] = 0;
+
+ return len;
+}
+
+static size_t get_record_print_text_size(struct printk_info *info,
+ unsigned int line_count,
+ bool syslog, bool time)
+{
+ char prefix[PREFIX_MAX];
+ size_t prefix_len;
+
+ prefix_len = info_print_prefix(info, syslog, time, prefix);
+
+ /*
+ * Each line will be preceded with a prefix. The intermediate
+ * newlines are already within the text, but a final trailing
+ * newline will be added.
+ */
+ return ((prefix_len * line_count) + info->text_len + 1);
+}
+
+/*
+ * Beginning with @start_seq, find the first record where it and all following
+ * records up to (but not including) @max_seq fit into @size.
+ *
+ * @max_seq is simply an upper bound and does not need to exist. If the caller
+ * does not require an upper bound, -1 can be used for @max_seq.
+ */
+static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
+ bool syslog, bool time)
+{
+ struct printk_info info;
+ unsigned int line_count;
+ size_t len = 0;
+ u64 seq;
+
+ /* Determine the size of the records up to @max_seq. */
+ prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+ if (info.seq >= max_seq)
+ break;
+ len += get_record_print_text_size(&info, line_count, syslog, time);
+ }
+
+ /*
+ * Adjust the upper bound for the next loop to avoid subtracting
+ * lengths that were never added.
+ */
+ if (seq < max_seq)
+ max_seq = seq;
+
+ /*
+ * Move first record forward until length fits into the buffer. Ignore
+ * newest messages that were not counted in the above cycle. Messages
+ * might appear and get lost in the meantime. This is a best effort
+ * that prevents an infinite loop that could occur with a retry.
+ */
+ prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+ if (len <= size || info.seq >= max_seq)
+ break;
+ len -= get_record_print_text_size(&info, line_count, syslog, time);
+ }
+
+ return seq;
+}
+
+/* The caller is responsible for making sure @size is greater than 0. */
+static int syslog_print(char __user *buf, int size)
+{
+ struct printk_info info;
+ struct printk_record r;
+ char *text;
+ int len = 0;
+ u64 seq;
+
+ text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
+ if (!text)
+ return -ENOMEM;
+
+ prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
+
+ mutex_lock(&syslog_lock);
+
+ /*
+ * Wait for the @syslog_seq record to be available. @syslog_seq may
+ * change while waiting.
+ */
+ do {
+ seq = syslog_seq;
+
+ mutex_unlock(&syslog_lock);
+ /*
+ * Guarantee this task is visible on the waitqueue before
+ * checking the wake condition.
+ *
+ * The full memory barrier within set_current_state() of
+ * prepare_to_wait_event() pairs with the full memory barrier
+ * within wq_has_sleeper().
+ *
+ * This pairs with __wake_up_klogd:A.
+ */
+ len = wait_event_interruptible(log_wait,
+ prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
+ mutex_lock(&syslog_lock);
+
+ if (len)
+ goto out;
+ } while (syslog_seq != seq);
+
+ /*
+ * Copy records that fit into the buffer. The above cycle makes sure
+ * that the first record is always available.
+ */
+ do {
+ size_t n;
+ size_t skip;
+ int err;
+
+ if (!prb_read_valid(prb, syslog_seq, &r))
+ break;
+
+ if (r.info->seq != syslog_seq) {
+ /* message is gone, move to next valid one */
+ syslog_seq = r.info->seq;
+ syslog_partial = 0;
+ }
+
+ /*
+ * To keep reading/counting partial line consistent,
+ * use printk_time value as of the beginning of a line.
+ */
+ if (!syslog_partial)
+ syslog_time = printk_time;
+
+ skip = syslog_partial;
+ n = record_print_text(&r, true, syslog_time);
+ if (n - syslog_partial <= size) {
+ /* message fits into buffer, move forward */
+ syslog_seq = r.info->seq + 1;
+ n -= syslog_partial;
+ syslog_partial = 0;
+ } else if (!len){
+ /* partial read(), remember position */
+ n = size;
+ syslog_partial += n;
+ } else
+ n = 0;
+
+ if (!n)
+ break;
+
+ mutex_unlock(&syslog_lock);
+ err = copy_to_user(buf, text + skip, n);
+ mutex_lock(&syslog_lock);
+
+ if (err) {
+ if (!len)
+ len = -EFAULT;
+ break;
+ }
+
+ len += n;
+ size -= n;
+ buf += n;
+ } while (size);
+out:
+ mutex_unlock(&syslog_lock);
+ kfree(text);
+ return len;
+}
+
+static int syslog_print_all(char __user *buf, int size, bool clear)
+{
+ struct printk_info info;
+ struct printk_record r;
+ char *text;
+ int len = 0;
+ u64 seq;
+ bool time;
+
+ text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
+ if (!text)
+ return -ENOMEM;
+
+ time = printk_time;
+ /*
+ * Find first record that fits, including all following records,
+ * into the user-provided buffer for this dump.
+ */
+ seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
+ size, true, time);
+
+ prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
+
+ len = 0;
+ prb_for_each_record(seq, prb, seq, &r) {
+ int textlen;
+
+ textlen = record_print_text(&r, true, time);
+
+ if (len + textlen > size) {
+ seq--;
+ break;
+ }
+
+ if (copy_to_user(buf + len, text, textlen))
+ len = -EFAULT;
+ else
+ len += textlen;
+
+ if (len < 0)
+ break;
+ }
+
+ if (clear) {
+ mutex_lock(&syslog_lock);
+ latched_seq_write(&clear_seq, seq);
+ mutex_unlock(&syslog_lock);
+ }
+
+ kfree(text);
+ return len;
+}
+
+static void syslog_clear(void)
+{
+ mutex_lock(&syslog_lock);
+ latched_seq_write(&clear_seq, prb_next_seq(prb));
+ mutex_unlock(&syslog_lock);
+}
+
+int do_syslog(int type, char __user *buf, int len, int source)
+{
+ struct printk_info info;
+ bool clear = false;
+ static int saved_console_loglevel = LOGLEVEL_DEFAULT;
+ int error;
+
+ error = check_syslog_permissions(type, source);
+ if (error)
+ return error;
+
+ switch (type) {
+ case SYSLOG_ACTION_CLOSE: /* Close log */
+ break;
+ case SYSLOG_ACTION_OPEN: /* Open log */
+ break;
+ case SYSLOG_ACTION_READ: /* Read from log */
+ if (!buf || len < 0)
+ return -EINVAL;
+ if (!len)
+ return 0;
+ if (!access_ok(buf, len))
+ return -EFAULT;
+ error = syslog_print(buf, len);
+ break;
+ /* Read/clear last kernel messages */
+ case SYSLOG_ACTION_READ_CLEAR:
+ clear = true;
+ fallthrough;
+ /* Read last kernel messages */
+ case SYSLOG_ACTION_READ_ALL:
+ if (!buf || len < 0)
+ return -EINVAL;
+ if (!len)
+ return 0;
+ if (!access_ok(buf, len))
+ return -EFAULT;
+ error = syslog_print_all(buf, len, clear);
+ break;
+ /* Clear ring buffer */
+ case SYSLOG_ACTION_CLEAR:
+ syslog_clear();
+ break;
+ /* Disable logging to console */
+ case SYSLOG_ACTION_CONSOLE_OFF:
+ if (saved_console_loglevel == LOGLEVEL_DEFAULT)
+ saved_console_loglevel = console_loglevel;
+ console_loglevel = minimum_console_loglevel;
+ break;
+ /* Enable logging to console */
+ case SYSLOG_ACTION_CONSOLE_ON:
+ if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
+ console_loglevel = saved_console_loglevel;
+ saved_console_loglevel = LOGLEVEL_DEFAULT;
+ }
+ break;
+ /* Set level of messages printed to console */
+ case SYSLOG_ACTION_CONSOLE_LEVEL:
+ if (len < 1 || len > 8)
+ return -EINVAL;
+ if (len < minimum_console_loglevel)
+ len = minimum_console_loglevel;
+ console_loglevel = len;
+ /* Implicitly re-enable logging to console */
+ saved_console_loglevel = LOGLEVEL_DEFAULT;
+ break;
+ /* Number of chars in the log buffer */
+ case SYSLOG_ACTION_SIZE_UNREAD:
+ mutex_lock(&syslog_lock);
+ if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
+ /* No unread messages. */
+ mutex_unlock(&syslog_lock);
+ return 0;
+ }
+ if (info.seq != syslog_seq) {
+ /* messages are gone, move to first one */
+ syslog_seq = info.seq;
+ syslog_partial = 0;
+ }
+ if (source == SYSLOG_FROM_PROC) {
+ /*
+ * Short-cut for poll(/"proc/kmsg") which simply checks
+ * for pending data, not the size; return the count of
+ * records, not the length.
+ */
+ error = prb_next_seq(prb) - syslog_seq;
+ } else {
+ bool time = syslog_partial ? syslog_time : printk_time;
+ unsigned int line_count;
+ u64 seq;
+
+ prb_for_each_info(syslog_seq, prb, seq, &info,
+ &line_count) {
+ error += get_record_print_text_size(&info, line_count,
+ true, time);
+ time = printk_time;
+ }
+ error -= syslog_partial;
+ }
+ mutex_unlock(&syslog_lock);
+ break;
+ /* Size of the log buffer */
+ case SYSLOG_ACTION_SIZE_BUFFER:
+ error = log_buf_len;
+ break;
+ default:
+ error = -EINVAL;
+ break;
+ }
+
+ return error;
+}
+
+SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
+{
+ return do_syslog(type, buf, len, SYSLOG_FROM_READER);
+}
+
+/*
+ * Special console_lock variants that help to reduce the risk of soft-lockups.
+ * They allow to pass console_lock to another printk() call using a busy wait.
+ */
+
+#ifdef CONFIG_LOCKDEP
+static struct lockdep_map console_owner_dep_map = {
+ .name = "console_owner"
+};
+#endif
+
+static DEFINE_RAW_SPINLOCK(console_owner_lock);
+static struct task_struct *console_owner;
+static bool console_waiter;
+
+/**
+ * console_lock_spinning_enable - mark beginning of code where another
+ * thread might safely busy wait
+ *
+ * This basically converts console_lock into a spinlock. This marks
+ * the section where the console_lock owner can not sleep, because
+ * there may be a waiter spinning (like a spinlock). Also it must be
+ * ready to hand over the lock at the end of the section.
+ */
+static void console_lock_spinning_enable(void)
+{
+ raw_spin_lock(&console_owner_lock);
+ console_owner = current;
+ raw_spin_unlock(&console_owner_lock);
+
+ /* The waiter may spin on us after setting console_owner */
+ spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
+}
+
+/**
+ * console_lock_spinning_disable_and_check - mark end of code where another
+ * thread was able to busy wait and check if there is a waiter
+ *
+ * This is called at the end of the section where spinning is allowed.
+ * It has two functions. First, it is a signal that it is no longer
+ * safe to start busy waiting for the lock. Second, it checks if
+ * there is a busy waiter and passes the lock rights to her.
+ *
+ * Important: Callers lose the lock if there was a busy waiter.
+ * They must not touch items synchronized by console_lock
+ * in this case.
+ *
+ * Return: 1 if the lock rights were passed, 0 otherwise.
+ */
+static int console_lock_spinning_disable_and_check(void)
+{
+ int waiter;
+
+ raw_spin_lock(&console_owner_lock);
+ waiter = READ_ONCE(console_waiter);
+ console_owner = NULL;
+ raw_spin_unlock(&console_owner_lock);
+
+ if (!waiter) {
+ spin_release(&console_owner_dep_map, _THIS_IP_);
+ return 0;
+ }
+
+ /* The waiter is now free to continue */
+ WRITE_ONCE(console_waiter, false);
+
+ spin_release(&console_owner_dep_map, _THIS_IP_);
+
+ /*
+ * Hand off console_lock to waiter. The waiter will perform
+ * the up(). After this, the waiter is the console_lock owner.
+ */
+ mutex_release(&console_lock_dep_map, _THIS_IP_);
+ return 1;
+}
+
+/**
+ * console_trylock_spinning - try to get console_lock by busy waiting
+ *
+ * This allows to busy wait for the console_lock when the current
+ * owner is running in specially marked sections. It means that
+ * the current owner is running and cannot reschedule until it
+ * is ready to lose the lock.
+ *
+ * Return: 1 if we got the lock, 0 othrewise
+ */
+static int console_trylock_spinning(void)
+{
+ struct task_struct *owner = NULL;
+ bool waiter;
+ bool spin = false;
+ unsigned long flags;
+
+ if (console_trylock())
+ return 1;
+
+ /*
+ * It's unsafe to spin once a panic has begun. If we are the
+ * panic CPU, we may have already halted the owner of the
+ * console_sem. If we are not the panic CPU, then we should
+ * avoid taking console_sem, so the panic CPU has a better
+ * chance of cleanly acquiring it later.
+ */
+ if (panic_in_progress())
+ return 0;
+
+ printk_safe_enter_irqsave(flags);
+
+ raw_spin_lock(&console_owner_lock);
+ owner = READ_ONCE(console_owner);
+ waiter = READ_ONCE(console_waiter);
+ if (!waiter && owner && owner != current) {
+ WRITE_ONCE(console_waiter, true);
+ spin = true;
+ }
+ raw_spin_unlock(&console_owner_lock);
+
+ /*
+ * If there is an active printk() writing to the
+ * consoles, instead of having it write our data too,
+ * see if we can offload that load from the active
+ * printer, and do some printing ourselves.
+ * Go into a spin only if there isn't already a waiter
+ * spinning, and there is an active printer, and
+ * that active printer isn't us (recursive printk?).
+ */
+ if (!spin) {
+ printk_safe_exit_irqrestore(flags);
+ return 0;
+ }
+
+ /* We spin waiting for the owner to release us */
+ spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
+ /* Owner will clear console_waiter on hand off */
+ while (READ_ONCE(console_waiter))
+ cpu_relax();
+ spin_release(&console_owner_dep_map, _THIS_IP_);
+
+ printk_safe_exit_irqrestore(flags);
+ /*
+ * The owner passed the console lock to us.
+ * Since we did not spin on console lock, annotate
+ * this as a trylock. Otherwise lockdep will
+ * complain.
+ */
+ mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
+
+ return 1;
+}
+
+/*
+ * Call the specified console driver, asking it to write out the specified
+ * text and length. If @dropped_text is non-NULL and any records have been
+ * dropped, a dropped message will be written out first.
+ */
+static void call_console_driver(struct console *con, const char *text, size_t len,
+ char *dropped_text)
+{
+ size_t dropped_len;
+
+ if (con->dropped && dropped_text) {
+ dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX,
+ "** %lu printk messages dropped **\n",
+ con->dropped);
+ con->dropped = 0;
+ con->write(con, dropped_text, dropped_len);
+ }
+
+ con->write(con, text, len);
+}
+
+/*
+ * Recursion is tracked separately on each CPU. If NMIs are supported, an
+ * additional NMI context per CPU is also separately tracked. Until per-CPU
+ * is available, a separate "early tracking" is performed.
+ */
+static DEFINE_PER_CPU(u8, printk_count);
+static u8 printk_count_early;
+#ifdef CONFIG_HAVE_NMI
+static DEFINE_PER_CPU(u8, printk_count_nmi);
+static u8 printk_count_nmi_early;
+#endif
+
+/*
+ * Recursion is limited to keep the output sane. printk() should not require
+ * more than 1 level of recursion (allowing, for example, printk() to trigger
+ * a WARN), but a higher value is used in case some printk-internal errors
+ * exist, such as the ringbuffer validation checks failing.
+ */
+#define PRINTK_MAX_RECURSION 3
+
+/*
+ * Return a pointer to the dedicated counter for the CPU+context of the
+ * caller.
+ */
+static u8 *__printk_recursion_counter(void)
+{
+#ifdef CONFIG_HAVE_NMI
+ if (in_nmi()) {
+ if (printk_percpu_data_ready())
+ return this_cpu_ptr(&printk_count_nmi);
+ return &printk_count_nmi_early;
+ }
+#endif
+ if (printk_percpu_data_ready())
+ return this_cpu_ptr(&printk_count);
+ return &printk_count_early;
+}
+
+/*
+ * Enter recursion tracking. Interrupts are disabled to simplify tracking.
+ * The caller must check the boolean return value to see if the recursion is
+ * allowed. On failure, interrupts are not disabled.
+ *
+ * @recursion_ptr must be a variable of type (u8 *) and is the same variable
+ * that is passed to printk_exit_irqrestore().
+ */
+#define printk_enter_irqsave(recursion_ptr, flags) \
+({ \
+ bool success = true; \
+ \
+ typecheck(u8 *, recursion_ptr); \
+ local_irq_save(flags); \
+ (recursion_ptr) = __printk_recursion_counter(); \
+ if (*(recursion_ptr) > PRINTK_MAX_RECURSION) { \
+ local_irq_restore(flags); \
+ success = false; \
+ } else { \
+ (*(recursion_ptr))++; \
+ } \
+ success; \
+})
+
+/* Exit recursion tracking, restoring interrupts. */
+#define printk_exit_irqrestore(recursion_ptr, flags) \
+ do { \
+ typecheck(u8 *, recursion_ptr); \
+ (*(recursion_ptr))--; \
+ local_irq_restore(flags); \
+ } while (0)
+
+int printk_delay_msec __read_mostly;
+
+static inline void printk_delay(int level)
+{
+ boot_delay_msec(level);
+
+ if (unlikely(printk_delay_msec)) {
+ int m = printk_delay_msec;
+
+ while (m--) {
+ mdelay(1);
+ touch_nmi_watchdog();
+ }
+ }
+}
+
+static inline u32 printk_caller_id(void)
+{
+ return in_task() ? task_pid_nr(current) :
+ 0x80000000 + smp_processor_id();
+}
+
+/**
+ * printk_parse_prefix - Parse level and control flags.
+ *
+ * @text: The terminated text message.
+ * @level: A pointer to the current level value, will be updated.
+ * @flags: A pointer to the current printk_info flags, will be updated.
+ *
+ * @level may be NULL if the caller is not interested in the parsed value.
+ * Otherwise the variable pointed to by @level must be set to
+ * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
+ *
+ * @flags may be NULL if the caller is not interested in the parsed value.
+ * Otherwise the variable pointed to by @flags will be OR'd with the parsed
+ * value.
+ *
+ * Return: The length of the parsed level and control flags.
+ */
+u16 printk_parse_prefix(const char *text, int *level,
+ enum printk_info_flags *flags)
+{
+ u16 prefix_len = 0;
+ int kern_level;
+
+ while (*text) {
+ kern_level = printk_get_level(text);
+ if (!kern_level)
+ break;
+
+ switch (kern_level) {
+ case '0' ... '7':
+ if (level && *level == LOGLEVEL_DEFAULT)
+ *level = kern_level - '0';
+ break;
+ case 'c': /* KERN_CONT */
+ if (flags)
+ *flags |= LOG_CONT;
+ }
+
+ prefix_len += 2;
+ text += 2;
+ }
+
+ return prefix_len;
+}
+
+__printf(5, 0)
+static u16 printk_sprint(char *text, u16 size, int facility,
+ enum printk_info_flags *flags, const char *fmt,
+ va_list args)
+{
+ u16 text_len;
+
+ text_len = vscnprintf(text, size, fmt, args);
+
+ /* Mark and strip a trailing newline. */
+ if (text_len && text[text_len - 1] == '\n') {
+ text_len--;
+ *flags |= LOG_NEWLINE;
+ }
+
+ /* Strip log level and control flags. */
+ if (facility == 0) {
+ u16 prefix_len;
+
+ prefix_len = printk_parse_prefix(text, NULL, NULL);
+ if (prefix_len) {
+ text_len -= prefix_len;
+ memmove(text, text + prefix_len, text_len);
+ }
+ }
+
+ trace_console_rcuidle(text, text_len);
+
+ return text_len;
+}
+
+__printf(4, 0)
+int vprintk_store(int facility, int level,
+ const struct dev_printk_info *dev_info,
+ const char *fmt, va_list args)
+{
+ struct prb_reserved_entry e;
+ enum printk_info_flags flags = 0;
+ struct printk_record r;
+ unsigned long irqflags;
+ u16 trunc_msg_len = 0;
+ char prefix_buf[8];
+ u8 *recursion_ptr;
+ u16 reserve_size;
+ va_list args2;
+ u32 caller_id;
+ u16 text_len;
+ int ret = 0;
+ u64 ts_nsec;
+
+ if (!printk_enter_irqsave(recursion_ptr, irqflags))
+ return 0;
+
+ /*
+ * Since the duration of printk() can vary depending on the message
+ * and state of the ringbuffer, grab the timestamp now so that it is
+ * close to the call of printk(). This provides a more deterministic
+ * timestamp with respect to the caller.
+ */
+ ts_nsec = local_clock();
+
+ caller_id = printk_caller_id();
+
+ /*
+ * The sprintf needs to come first since the syslog prefix might be
+ * passed in as a parameter. An extra byte must be reserved so that
+ * later the vscnprintf() into the reserved buffer has room for the
+ * terminating '\0', which is not counted by vsnprintf().
+ */
+ va_copy(args2, args);
+ reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
+ va_end(args2);
+
+ if (reserve_size > LOG_LINE_MAX)
+ reserve_size = LOG_LINE_MAX;
+
+ /* Extract log level or control flags. */
+ if (facility == 0)
+ printk_parse_prefix(&prefix_buf[0], &level, &flags);
+
+ if (level == LOGLEVEL_DEFAULT)
+ level = default_message_loglevel;
+
+ if (dev_info)
+ flags |= LOG_NEWLINE;
+
+ if (flags & LOG_CONT) {
+ prb_rec_init_wr(&r, reserve_size);
+ if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
+ text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
+ facility, &flags, fmt, args);
+ r.info->text_len += text_len;
+
+ if (flags & LOG_NEWLINE) {
+ r.info->flags |= LOG_NEWLINE;
+ prb_final_commit(&e);
+ } else {
+ prb_commit(&e);
+ }
+
+ ret = text_len;
+ goto out;
+ }
+ }
+
+ /*
+ * Explicitly initialize the record before every prb_reserve() call.
+ * prb_reserve_in_last() and prb_reserve() purposely invalidate the
+ * structure when they fail.
+ */
+ prb_rec_init_wr(&r, reserve_size);
+ if (!prb_reserve(&e, prb, &r)) {
+ /* truncate the message if it is too long for empty buffer */
+ truncate_msg(&reserve_size, &trunc_msg_len);
+
+ prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
+ if (!prb_reserve(&e, prb, &r))
+ goto out;
+ }
+
+ /* fill message */
+ text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
+ if (trunc_msg_len)
+ memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
+ r.info->text_len = text_len + trunc_msg_len;
+ r.info->facility = facility;
+ r.info->level = level & 7;
+ r.info->flags = flags & 0x1f;
+ r.info->ts_nsec = ts_nsec;
+ r.info->caller_id = caller_id;
+ if (dev_info)
+ memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
+
+ /* A message without a trailing newline can be continued. */
+ if (!(flags & LOG_NEWLINE))
+ prb_commit(&e);
+ else
+ prb_final_commit(&e);
+
+ ret = text_len + trunc_msg_len;
+out:
+ printk_exit_irqrestore(recursion_ptr, irqflags);
+ return ret;
+}
+
+asmlinkage int vprintk_emit(int facility, int level,
+ const struct dev_printk_info *dev_info,
+ const char *fmt, va_list args)
+{
+ int printed_len;
+ bool in_sched = false;
+
+ /* Suppress unimportant messages after panic happens */
+ if (unlikely(suppress_printk))
+ return 0;
+
+ if (unlikely(suppress_panic_printk) &&
+ atomic_read(&panic_cpu) != raw_smp_processor_id())
+ return 0;
+
+ if (level == LOGLEVEL_SCHED) {
+ level = LOGLEVEL_DEFAULT;
+ in_sched = true;
+ }
+
+ printk_delay(level);
+
+ printed_len = vprintk_store(facility, level, dev_info, fmt, args);
+
+ /* If called from the scheduler, we can not call up(). */
+ if (!in_sched) {
+ /*
+ * The caller may be holding system-critical or
+ * timing-sensitive locks. Disable preemption during
+ * printing of all remaining records to all consoles so that
+ * this context can return as soon as possible. Hopefully
+ * another printk() caller will take over the printing.
+ */
+ preempt_disable();
+ /*
+ * Try to acquire and then immediately release the console
+ * semaphore. The release will print out buffers. With the
+ * spinning variant, this context tries to take over the
+ * printing from another printing context.
+ */
+ if (console_trylock_spinning())
+ console_unlock();
+ preempt_enable();
+ }
+
+ if (in_sched)
+ defer_console_output();
+ else
+ wake_up_klogd();
+
+ return printed_len;
+}
+EXPORT_SYMBOL(vprintk_emit);
+
+int vprintk_default(const char *fmt, va_list args)
+{
+ return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
+}
+EXPORT_SYMBOL_GPL(vprintk_default);
+
+asmlinkage __visible int _printk(const char *fmt, ...)
+{
+ va_list args;
+ int r;
+
+ va_start(args, fmt);
+ r = vprintk(fmt, args);
+ va_end(args);
+
+ return r;
+}
+EXPORT_SYMBOL(_printk);
+
+static bool pr_flush(int timeout_ms, bool reset_on_progress);
+static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
+
+#else /* CONFIG_PRINTK */
+
+#define CONSOLE_LOG_MAX 0
+#define DROPPED_TEXT_MAX 0
+#define printk_time false
+
+#define prb_read_valid(rb, seq, r) false
+#define prb_first_valid_seq(rb) 0
+#define prb_next_seq(rb) 0
+
+static u64 syslog_seq;
+
+static size_t record_print_text(const struct printk_record *r,
+ bool syslog, bool time)
+{
+ return 0;
+}
+static ssize_t info_print_ext_header(char *buf, size_t size,
+ struct printk_info *info)
+{
+ return 0;
+}
+static ssize_t msg_print_ext_body(char *buf, size_t size,
+ char *text, size_t text_len,
+ struct dev_printk_info *dev_info) { return 0; }
+static void console_lock_spinning_enable(void) { }
+static int console_lock_spinning_disable_and_check(void) { return 0; }
+static void call_console_driver(struct console *con, const char *text, size_t len,
+ char *dropped_text)
+{
+}
+static bool suppress_message_printing(int level) { return false; }
+static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
+static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
+
+#endif /* CONFIG_PRINTK */
+
+#ifdef CONFIG_EARLY_PRINTK
+struct console *early_console;
+
+asmlinkage __visible void early_printk(const char *fmt, ...)
+{
+ va_list ap;
+ char buf[512];
+ int n;
+
+ if (!early_console)
+ return;
+
+ va_start(ap, fmt);
+ n = vscnprintf(buf, sizeof(buf), fmt, ap);
+ va_end(ap);
+
+ early_console->write(early_console, buf, n);
+}
+#endif
+
+static void set_user_specified(struct console_cmdline *c, bool user_specified)
+{
+ if (!user_specified)
+ return;
+
+ /*
+ * @c console was defined by the user on the command line.
+ * Do not clear when added twice also by SPCR or the device tree.
+ */
+ c->user_specified = true;
+ /* At least one console defined by the user on the command line. */
+ console_set_on_cmdline = 1;
+}
+
+static int __add_preferred_console(char *name, int idx, char *options,
+ char *brl_options, bool user_specified)
+{
+ struct console_cmdline *c;
+ int i;
+
+ /*
+ * See if this tty is not yet registered, and
+ * if we have a slot free.
+ */
+ for (i = 0, c = console_cmdline;
+ i < MAX_CMDLINECONSOLES && c->name[0];
+ i++, c++) {
+ if (strcmp(c->name, name) == 0 && c->index == idx) {
+ if (!brl_options)
+ preferred_console = i;
+ set_user_specified(c, user_specified);
+ return 0;
+ }
+ }
+ if (i == MAX_CMDLINECONSOLES)
+ return -E2BIG;
+ if (!brl_options)
+ preferred_console = i;
+ strlcpy(c->name, name, sizeof(c->name));
+ c->options = options;
+ set_user_specified(c, user_specified);
+ braille_set_options(c, brl_options);
+
+ c->index = idx;
+ return 0;
+}
+
+static int __init console_msg_format_setup(char *str)
+{
+ if (!strcmp(str, "syslog"))
+ console_msg_format = MSG_FORMAT_SYSLOG;
+ if (!strcmp(str, "default"))
+ console_msg_format = MSG_FORMAT_DEFAULT;
+ return 1;
+}
+__setup("console_msg_format=", console_msg_format_setup);
+
+/*
+ * Set up a console. Called via do_early_param() in init/main.c
+ * for each "console=" parameter in the boot command line.
+ */
+static int __init console_setup(char *str)
+{
+ char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
+ char *s, *options, *brl_options = NULL;
+ int idx;
+
+ /*
+ * console="" or console=null have been suggested as a way to
+ * disable console output. Use ttynull that has been created
+ * for exactly this purpose.
+ */
+ if (str[0] == 0 || strcmp(str, "null") == 0) {
+ __add_preferred_console("ttynull", 0, NULL, NULL, true);
+ return 1;
+ }
+
+ if (_braille_console_setup(&str, &brl_options))
+ return 1;
+
+ /*
+ * Decode str into name, index, options.
+ */
+ if (str[0] >= '0' && str[0] <= '9') {
+ strcpy(buf, "ttyS");
+ strncpy(buf + 4, str, sizeof(buf) - 5);
+ } else {
+ strncpy(buf, str, sizeof(buf) - 1);
+ }
+ buf[sizeof(buf) - 1] = 0;
+ options = strchr(str, ',');
+ if (options)
+ *(options++) = 0;
+#ifdef __sparc__
+ if (!strcmp(str, "ttya"))
+ strcpy(buf, "ttyS0");
+ if (!strcmp(str, "ttyb"))
+ strcpy(buf, "ttyS1");
+#endif
+ for (s = buf; *s; s++)
+ if (isdigit(*s) || *s == ',')
+ break;
+ idx = simple_strtoul(s, NULL, 10);
+ *s = 0;
+
+ __add_preferred_console(buf, idx, options, brl_options, true);
+ return 1;
+}
+__setup("console=", console_setup);
+
+/**
+ * add_preferred_console - add a device to the list of preferred consoles.
+ * @name: device name
+ * @idx: device index
+ * @options: options for this console
+ *
+ * The last preferred console added will be used for kernel messages
+ * and stdin/out/err for init. Normally this is used by console_setup
+ * above to handle user-supplied console arguments; however it can also
+ * be used by arch-specific code either to override the user or more
+ * commonly to provide a default console (ie from PROM variables) when
+ * the user has not supplied one.
+ */
+int add_preferred_console(char *name, int idx, char *options)
+{
+ return __add_preferred_console(name, idx, options, NULL, false);
+}
+
+bool console_suspend_enabled = true;
+EXPORT_SYMBOL(console_suspend_enabled);
+
+static int __init console_suspend_disable(char *str)
+{
+ console_suspend_enabled = false;
+ return 1;
+}
+__setup("no_console_suspend", console_suspend_disable);
+module_param_named(console_suspend, console_suspend_enabled,
+ bool, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
+ " and hibernate operations");
+
+static bool printk_console_no_auto_verbose;
+
+void console_verbose(void)
+{
+ if (console_loglevel && !printk_console_no_auto_verbose)
+ console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
+}
+EXPORT_SYMBOL_GPL(console_verbose);
+
+module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
+MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
+
+/**
+ * suspend_console - suspend the console subsystem
+ *
+ * This disables printk() while we go into suspend states
+ */
+void suspend_console(void)
+{
+ if (!console_suspend_enabled)
+ return;
+ pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
+ pr_flush(1000, true);
+ console_lock();
+ console_suspended = 1;
+ up_console_sem();
+}
+
+void resume_console(void)
+{
+ if (!console_suspend_enabled)
+ return;
+ down_console_sem();
+ console_suspended = 0;
+ console_unlock();
+ pr_flush(1000, true);
+}
+
+/**
+ * console_cpu_notify - print deferred console messages after CPU hotplug
+ * @cpu: unused
+ *
+ * If printk() is called from a CPU that is not online yet, the messages
+ * will be printed on the console only if there are CON_ANYTIME consoles.
+ * This function is called when a new CPU comes online (or fails to come
+ * up) or goes offline.
+ */
+static int console_cpu_notify(unsigned int cpu)
+{
+ if (!cpuhp_tasks_frozen) {
+ /* If trylock fails, someone else is doing the printing */
+ if (console_trylock())
+ console_unlock();
+ }
+ return 0;
+}
+
+/*
+ * Return true when this CPU should unlock console_sem without pushing all
+ * messages to the console. This reduces the chance that the console is
+ * locked when the panic CPU tries to use it.
+ */
+static bool abandon_console_lock_in_panic(void)
+{
+ if (!panic_in_progress())
+ return false;
+
+ /*
+ * We can use raw_smp_processor_id() here because it is impossible for
+ * the task to be migrated to the panic_cpu, or away from it. If
+ * panic_cpu has already been set, and we're not currently executing on
+ * that CPU, then we never will be.
+ */
+ return atomic_read(&panic_cpu) != raw_smp_processor_id();
+}
+
+/**
+ * console_lock - lock the console system for exclusive use.
+ *
+ * Acquires a lock which guarantees that the caller has
+ * exclusive access to the console system and the console_drivers list.
+ *
+ * Can sleep, returns nothing.
+ */
+void console_lock(void)
+{
+ might_sleep();
+
+ /* On panic, the console_lock must be left to the panic cpu. */
+ while (abandon_console_lock_in_panic())
+ msleep(1000);
+
+ down_console_sem();
+ if (console_suspended)
+ return;
+ console_locked = 1;
+ console_may_schedule = 1;
+}
+EXPORT_SYMBOL(console_lock);
+
+/**
+ * console_trylock - try to lock the console system for exclusive use.
+ *
+ * Try to acquire a lock which guarantees that the caller has exclusive
+ * access to the console system and the console_drivers list.
+ *
+ * returns 1 on success, and 0 on failure to acquire the lock.
+ */
+int console_trylock(void)
+{
+ /* On panic, the console_lock must be left to the panic cpu. */
+ if (abandon_console_lock_in_panic())
+ return 0;
+ if (down_trylock_console_sem())
+ return 0;
+ if (console_suspended) {
+ up_console_sem();
+ return 0;
+ }
+ console_locked = 1;
+ console_may_schedule = 0;
+ return 1;
+}
+EXPORT_SYMBOL(console_trylock);
+
+int is_console_locked(void)
+{
+ return console_locked;
+}
+EXPORT_SYMBOL(is_console_locked);
+
+/*
+ * Check if the given console is currently capable and allowed to print
+ * records.
+ *
+ * Requires the console_lock.
+ */
+static inline bool console_is_usable(struct console *con)
+{
+ if (!(con->flags & CON_ENABLED))
+ return false;
+
+ if (!con->write)
+ return false;
+
+ /*
+ * Console drivers may assume that per-cpu resources have been
+ * allocated. So unless they're explicitly marked as being able to
+ * cope (CON_ANYTIME) don't call them until this CPU is officially up.
+ */
+ if (!cpu_online(raw_smp_processor_id()) &&
+ !(con->flags & CON_ANYTIME))
+ return false;
+
+ return true;
+}
+
+static void __console_unlock(void)
+{
+ console_locked = 0;
+ up_console_sem();
+}
+
+/*
+ * Print one record for the given console. The record printed is whatever
+ * record is the next available record for the given console.
+ *
+ * @text is a buffer of size CONSOLE_LOG_MAX.
+ *
+ * If extended messages should be printed, @ext_text is a buffer of size
+ * CONSOLE_EXT_LOG_MAX. Otherwise @ext_text must be NULL.
+ *
+ * If dropped messages should be printed, @dropped_text is a buffer of size
+ * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
+ *
+ * @handover will be set to true if a printk waiter has taken over the
+ * console_lock, in which case the caller is no longer holding the
+ * console_lock. Otherwise it is set to false.
+ *
+ * Returns false if the given console has no next record to print, otherwise
+ * true.
+ *
+ * Requires the console_lock.
+ */
+static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
+ char *dropped_text, bool *handover)
+{
+ static int panic_console_dropped;
+ struct printk_info info;
+ struct printk_record r;
+ unsigned long flags;
+ char *write_text;
+ size_t len;
+
+ prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
+
+ *handover = false;
+
+ if (!prb_read_valid(prb, con->seq, &r))
+ return false;
+
+ if (con->seq != r.info->seq) {
+ con->dropped += r.info->seq - con->seq;
+ con->seq = r.info->seq;
+ if (panic_in_progress() && panic_console_dropped++ > 10) {
+ suppress_panic_printk = 1;
+ pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
+ }
+ }
+
+ /* Skip record that has level above the console loglevel. */
+ if (suppress_message_printing(r.info->level)) {
+ con->seq++;
+ goto skip;
+ }
+
+ if (ext_text) {
+ write_text = ext_text;
+ len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info);
+ len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len,
+ &r.text_buf[0], r.info->text_len, &r.info->dev_info);
+ } else {
+ write_text = text;
+ len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
+ }
+
+ /*
+ * While actively printing out messages, if another printk()
+ * were to occur on another CPU, it may wait for this one to
+ * finish. This task can not be preempted if there is a
+ * waiter waiting to take over.
+ *
+ * Interrupts are disabled because the hand over to a waiter
+ * must not be interrupted until the hand over is completed
+ * (@console_waiter is cleared).
+ */
+ printk_safe_enter_irqsave(flags);
+ console_lock_spinning_enable();
+
+ stop_critical_timings(); /* don't trace print latency */
+ call_console_driver(con, write_text, len, dropped_text);
+ start_critical_timings();
+
+ con->seq++;
+
+ *handover = console_lock_spinning_disable_and_check();
+ printk_safe_exit_irqrestore(flags);
+skip:
+ return true;
+}
+
+/*
+ * Print out all remaining records to all consoles.
+ *
+ * @do_cond_resched is set by the caller. It can be true only in schedulable
+ * context.
+ *
+ * @next_seq is set to the sequence number after the last available record.
+ * The value is valid only when this function returns true. It means that all
+ * usable consoles are completely flushed.
+ *
+ * @handover will be set to true if a printk waiter has taken over the
+ * console_lock, in which case the caller is no longer holding the
+ * console_lock. Otherwise it is set to false.
+ *
+ * Returns true when there was at least one usable console and all messages
+ * were flushed to all usable consoles. A returned false informs the caller
+ * that everything was not flushed (either there were no usable consoles or
+ * another context has taken over printing or it is a panic situation and this
+ * is not the panic CPU). Regardless the reason, the caller should assume it
+ * is not useful to immediately try again.
+ *
+ * Requires the console_lock.
+ */
+static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
+{
+ static char dropped_text[DROPPED_TEXT_MAX];
+ static char ext_text[CONSOLE_EXT_LOG_MAX];
+ static char text[CONSOLE_LOG_MAX];
+ bool any_usable = false;
+ struct console *con;
+ bool any_progress;
+
+ *next_seq = 0;
+ *handover = false;
+
+ do {
+ any_progress = false;
+
+ for_each_console(con) {
+ bool progress;
+
+ if (!console_is_usable(con))
+ continue;
+ any_usable = true;
+
+ if (con->flags & CON_EXTENDED) {
+ /* Extended consoles do not print "dropped messages". */
+ progress = console_emit_next_record(con, &text[0],
+ &ext_text[0], NULL,
+ handover);
+ } else {
+ progress = console_emit_next_record(con, &text[0],
+ NULL, &dropped_text[0],
+ handover);
+ }
+ if (*handover)
+ return false;
+
+ /* Track the next of the highest seq flushed. */
+ if (con->seq > *next_seq)
+ *next_seq = con->seq;
+
+ if (!progress)
+ continue;
+ any_progress = true;
+
+ /* Allow panic_cpu to take over the consoles safely. */
+ if (abandon_console_lock_in_panic())
+ return false;
+
+ if (do_cond_resched)
+ cond_resched();
+ }
+ } while (any_progress);
+
+ return any_usable;
+}
+
+/**
+ * console_unlock - unlock the console system
+ *
+ * Releases the console_lock which the caller holds on the console system
+ * and the console driver list.
+ *
+ * While the console_lock was held, console output may have been buffered
+ * by printk(). If this is the case, console_unlock(); emits
+ * the output prior to releasing the lock.
+ *
+ * console_unlock(); may be called from any context.
+ */
+void console_unlock(void)
+{
+ bool do_cond_resched;
+ bool handover;
+ bool flushed;
+ u64 next_seq;
+
+ if (console_suspended) {
+ up_console_sem();
+ return;
+ }
+
+ /*
+ * Console drivers are called with interrupts disabled, so
+ * @console_may_schedule should be cleared before; however, we may
+ * end up dumping a lot of lines, for example, if called from
+ * console registration path, and should invoke cond_resched()
+ * between lines if allowable. Not doing so can cause a very long
+ * scheduling stall on a slow console leading to RCU stall and
+ * softlockup warnings which exacerbate the issue with more
+ * messages practically incapacitating the system. Therefore, create
+ * a local to use for the printing loop.
+ */
+ do_cond_resched = console_may_schedule;
+
+ do {
+ console_may_schedule = 0;
+
+ flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
+ if (!handover)
+ __console_unlock();
+
+ /*
+ * Abort if there was a failure to flush all messages to all
+ * usable consoles. Either it is not possible to flush (in
+ * which case it would be an infinite loop of retrying) or
+ * another context has taken over printing.
+ */
+ if (!flushed)
+ break;
+
+ /*
+ * Some context may have added new records after
+ * console_flush_all() but before unlocking the console.
+ * Re-check if there is a new record to flush. If the trylock
+ * fails, another context is already handling the printing.
+ */
+ } while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
+}
+EXPORT_SYMBOL(console_unlock);
+
+/**
+ * console_conditional_schedule - yield the CPU if required
+ *
+ * If the console code is currently allowed to sleep, and
+ * if this CPU should yield the CPU to another task, do
+ * so here.
+ *
+ * Must be called within console_lock();.
+ */
+void __sched console_conditional_schedule(void)
+{
+ if (console_may_schedule)
+ cond_resched();
+}
+EXPORT_SYMBOL(console_conditional_schedule);
+
+void console_unblank(void)
+{
+ struct console *c;
+
+ /*
+ * console_unblank can no longer be called in interrupt context unless
+ * oops_in_progress is set to 1..
+ */
+ if (oops_in_progress) {
+ if (down_trylock_console_sem() != 0)
+ return;
+ } else
+ console_lock();
+
+ console_locked = 1;
+ console_may_schedule = 0;
+ for_each_console(c)
+ if ((c->flags & CON_ENABLED) && c->unblank)
+ c->unblank();
+ console_unlock();
+
+ if (!oops_in_progress)
+ pr_flush(1000, true);
+}
+
+/**
+ * console_flush_on_panic - flush console content on panic
+ * @mode: flush all messages in buffer or just the pending ones
+ *
+ * Immediately output all pending messages no matter what.
+ */
+void console_flush_on_panic(enum con_flush_mode mode)
+{
+ /*
+ * If someone else is holding the console lock, trylock will fail
+ * and may_schedule may be set. Ignore and proceed to unlock so
+ * that messages are flushed out. As this can be called from any
+ * context and we don't want to get preempted while flushing,
+ * ensure may_schedule is cleared.
+ */
+ console_trylock();
+ console_may_schedule = 0;
+
+ if (mode == CONSOLE_REPLAY_ALL) {
+ struct console *c;
+ u64 seq;
+
+ seq = prb_first_valid_seq(prb);
+ for_each_console(c)
+ c->seq = seq;
+ }
+ console_unlock();
+}
+
+/*
+ * Return the console tty driver structure and its associated index
+ */
+struct tty_driver *console_device(int *index)
+{
+ struct console *c;
+ struct tty_driver *driver = NULL;
+
+ console_lock();
+ for_each_console(c) {
+ if (!c->device)
+ continue;
+ driver = c->device(c, index);
+ if (driver)
+ break;
+ }
+ console_unlock();
+ return driver;
+}
+
+/*
+ * Prevent further output on the passed console device so that (for example)
+ * serial drivers can disable console output before suspending a port, and can
+ * re-enable output afterwards.
+ */
+void console_stop(struct console *console)
+{
+ __pr_flush(console, 1000, true);
+ console_lock();
+ console->flags &= ~CON_ENABLED;
+ console_unlock();
+}
+EXPORT_SYMBOL(console_stop);
+
+void console_start(struct console *console)
+{
+ console_lock();
+ console->flags |= CON_ENABLED;
+ console_unlock();
+ __pr_flush(console, 1000, true);
+}
+EXPORT_SYMBOL(console_start);
+
+static int __read_mostly keep_bootcon;
+
+static int __init keep_bootcon_setup(char *str)
+{
+ keep_bootcon = 1;
+ pr_info("debug: skip boot console de-registration.\n");
+
+ return 0;
+}
+
+early_param("keep_bootcon", keep_bootcon_setup);
+
+/*
+ * This is called by register_console() to try to match
+ * the newly registered console with any of the ones selected
+ * by either the command line or add_preferred_console() and
+ * setup/enable it.
+ *
+ * Care need to be taken with consoles that are statically
+ * enabled such as netconsole
+ */
+static int try_enable_preferred_console(struct console *newcon,
+ bool user_specified)
+{
+ struct console_cmdline *c;
+ int i, err;
+
+ for (i = 0, c = console_cmdline;
+ i < MAX_CMDLINECONSOLES && c->name[0];
+ i++, c++) {
+ if (c->user_specified != user_specified)
+ continue;
+ if (!newcon->match ||
+ newcon->match(newcon, c->name, c->index, c->options) != 0) {
+ /* default matching */
+ BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
+ if (strcmp(c->name, newcon->name) != 0)
+ continue;
+ if (newcon->index >= 0 &&
+ newcon->index != c->index)
+ continue;
+ if (newcon->index < 0)
+ newcon->index = c->index;
+
+ if (_braille_register_console(newcon, c))
+ return 0;
+
+ if (newcon->setup &&
+ (err = newcon->setup(newcon, c->options)) != 0)
+ return err;
+ }
+ newcon->flags |= CON_ENABLED;
+ if (i == preferred_console)
+ newcon->flags |= CON_CONSDEV;
+ return 0;
+ }
+
+ /*
+ * Some consoles, such as pstore and netconsole, can be enabled even
+ * without matching. Accept the pre-enabled consoles only when match()
+ * and setup() had a chance to be called.
+ */
+ if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
+ return 0;
+
+ return -ENOENT;
+}
+
+/* Try to enable the console unconditionally */
+static void try_enable_default_console(struct console *newcon)
+{
+ if (newcon->index < 0)
+ newcon->index = 0;
+
+ if (newcon->setup && newcon->setup(newcon, NULL) != 0)
+ return;
+
+ newcon->flags |= CON_ENABLED;
+
+ if (newcon->device)
+ newcon->flags |= CON_CONSDEV;
+}
+
+#define con_printk(lvl, con, fmt, ...) \
+ printk(lvl pr_fmt("%sconsole [%s%d] " fmt), \
+ (con->flags & CON_BOOT) ? "boot" : "", \
+ con->name, con->index, ##__VA_ARGS__)
+
+/*
+ * The console driver calls this routine during kernel initialization
+ * to register the console printing procedure with printk() and to
+ * print any messages that were printed by the kernel before the
+ * console driver was initialized.
+ *
+ * This can happen pretty early during the boot process (because of
+ * early_printk) - sometimes before setup_arch() completes - be careful
+ * of what kernel features are used - they may not be initialised yet.
+ *
+ * There are two types of consoles - bootconsoles (early_printk) and
+ * "real" consoles (everything which is not a bootconsole) which are
+ * handled differently.
+ * - Any number of bootconsoles can be registered at any time.
+ * - As soon as a "real" console is registered, all bootconsoles
+ * will be unregistered automatically.
+ * - Once a "real" console is registered, any attempt to register a
+ * bootconsoles will be rejected
+ */
+void register_console(struct console *newcon)
+{
+ struct console *con;
+ bool bootcon_enabled = false;
+ bool realcon_enabled = false;
+ int err;
+
+ for_each_console(con) {
+ if (WARN(con == newcon, "console '%s%d' already registered\n",
+ con->name, con->index))
+ return;
+ }
+
+ for_each_console(con) {
+ if (con->flags & CON_BOOT)
+ bootcon_enabled = true;
+ else
+ realcon_enabled = true;
+ }
+
+ /* Do not register boot consoles when there already is a real one. */
+ if (newcon->flags & CON_BOOT && realcon_enabled) {
+ pr_info("Too late to register bootconsole %s%d\n",
+ newcon->name, newcon->index);
+ return;
+ }
+
+ /*
+ * See if we want to enable this console driver by default.
+ *
+ * Nope when a console is preferred by the command line, device
+ * tree, or SPCR.
+ *
+ * The first real console with tty binding (driver) wins. More
+ * consoles might get enabled before the right one is found.
+ *
+ * Note that a console with tty binding will have CON_CONSDEV
+ * flag set and will be first in the list.
+ */
+ if (preferred_console < 0) {
+ if (!console_drivers || !console_drivers->device ||
+ console_drivers->flags & CON_BOOT) {
+ try_enable_default_console(newcon);
+ }
+ }
+
+ /* See if this console matches one we selected on the command line */
+ err = try_enable_preferred_console(newcon, true);
+
+ /* If not, try to match against the platform default(s) */
+ if (err == -ENOENT)
+ err = try_enable_preferred_console(newcon, false);
+
+ /* printk() messages are not printed to the Braille console. */
+ if (err || newcon->flags & CON_BRL)
+ return;
+
+ /*
+ * If we have a bootconsole, and are switching to a real console,
+ * don't print everything out again, since when the boot console, and
+ * the real console are the same physical device, it's annoying to
+ * see the beginning boot messages twice
+ */
+ if (bootcon_enabled &&
+ ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
+ newcon->flags &= ~CON_PRINTBUFFER;
+ }
+
+ /*
+ * Put this console in the list - keep the
+ * preferred driver at the head of the list.
+ */
+ console_lock();
+ if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
+ newcon->next = console_drivers;
+ console_drivers = newcon;
+ if (newcon->next)
+ newcon->next->flags &= ~CON_CONSDEV;
+ /* Ensure this flag is always set for the head of the list */
+ newcon->flags |= CON_CONSDEV;
+ } else {
+ newcon->next = console_drivers->next;
+ console_drivers->next = newcon;
+ }
+
+ newcon->dropped = 0;
+ if (newcon->flags & CON_PRINTBUFFER) {
+ /* Get a consistent copy of @syslog_seq. */
+ mutex_lock(&syslog_lock);
+ newcon->seq = syslog_seq;
+ mutex_unlock(&syslog_lock);
+ } else {
+ /* Begin with next message. */
+ newcon->seq = prb_next_seq(prb);
+ }
+ console_unlock();
+ console_sysfs_notify();
+
+ /*
+ * By unregistering the bootconsoles after we enable the real console
+ * we get the "console xxx enabled" message on all the consoles -
+ * boot consoles, real consoles, etc - this is to ensure that end
+ * users know there might be something in the kernel's log buffer that
+ * went to the bootconsole (that they do not see on the real console)
+ */
+ con_printk(KERN_INFO, newcon, "enabled\n");
+ if (bootcon_enabled &&
+ ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
+ !keep_bootcon) {
+ for_each_console(con)
+ if (con->flags & CON_BOOT)
+ unregister_console(con);
+ }
+}
+EXPORT_SYMBOL(register_console);
+
+int unregister_console(struct console *console)
+{
+ struct console *con;
+ int res;
+
+ con_printk(KERN_INFO, console, "disabled\n");
+
+ res = _braille_unregister_console(console);
+ if (res < 0)
+ return res;
+ if (res > 0)
+ return 0;
+
+ res = -ENODEV;
+ console_lock();
+ if (console_drivers == console) {
+ console_drivers=console->next;
+ res = 0;
+ } else {
+ for_each_console(con) {
+ if (con->next == console) {
+ con->next = console->next;
+ res = 0;
+ break;
+ }
+ }
+ }
+
+ if (res)
+ goto out_disable_unlock;
+
+ /*
+ * If this isn't the last console and it has CON_CONSDEV set, we
+ * need to set it on the next preferred console.
+ */
+ if (console_drivers != NULL && console->flags & CON_CONSDEV)
+ console_drivers->flags |= CON_CONSDEV;
+
+ console->flags &= ~CON_ENABLED;
+ console_unlock();
+ console_sysfs_notify();
+
+ if (console->exit)
+ res = console->exit(console);
+
+ return res;
+
+out_disable_unlock:
+ console->flags &= ~CON_ENABLED;
+ console_unlock();
+
+ return res;
+}
+EXPORT_SYMBOL(unregister_console);
+
+/*
+ * Initialize the console device. This is called *early*, so
+ * we can't necessarily depend on lots of kernel help here.
+ * Just do some early initializations, and do the complex setup
+ * later.
+ */
+void __init console_init(void)
+{
+ int ret;
+ initcall_t call;
+ initcall_entry_t *ce;
+
+ /* Setup the default TTY line discipline. */
+ n_tty_init();
+
+ /*
+ * set up the console device so that later boot sequences can
+ * inform about problems etc..
+ */
+ ce = __con_initcall_start;
+ trace_initcall_level("console");
+ while (ce < __con_initcall_end) {
+ call = initcall_from_entry(ce);
+ trace_initcall_start(call);
+ ret = call();
+ trace_initcall_finish(call, ret);
+ ce++;
+ }
+}
+
+/*
+ * Some boot consoles access data that is in the init section and which will
+ * be discarded after the initcalls have been run. To make sure that no code
+ * will access this data, unregister the boot consoles in a late initcall.
+ *
+ * If for some reason, such as deferred probe or the driver being a loadable
+ * module, the real console hasn't registered yet at this point, there will
+ * be a brief interval in which no messages are logged to the console, which
+ * makes it difficult to diagnose problems that occur during this time.
+ *
+ * To mitigate this problem somewhat, only unregister consoles whose memory
+ * intersects with the init section. Note that all other boot consoles will
+ * get unregistered when the real preferred console is registered.
+ */
+static int __init printk_late_init(void)
+{
+ struct console *con;
+ int ret;
+
+ for_each_console(con) {
+ if (!(con->flags & CON_BOOT))
+ continue;
+
+ /* Check addresses that might be used for enabled consoles. */
+ if (init_section_intersects(con, sizeof(*con)) ||
+ init_section_contains(con->write, 0) ||
+ init_section_contains(con->read, 0) ||
+ init_section_contains(con->device, 0) ||
+ init_section_contains(con->unblank, 0) ||
+ init_section_contains(con->data, 0)) {
+ /*
+ * Please, consider moving the reported consoles out
+ * of the init section.
+ */
+ pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
+ con->name, con->index);
+ unregister_console(con);
+ }
+ }
+ ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
+ console_cpu_notify);
+ WARN_ON(ret < 0);
+ ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
+ console_cpu_notify, NULL);
+ WARN_ON(ret < 0);
+ printk_sysctl_init();
+ return 0;
+}
+late_initcall(printk_late_init);
+
+#if defined CONFIG_PRINTK
+/* If @con is specified, only wait for that console. Otherwise wait for all. */
+static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
+{
+ int remaining = timeout_ms;
+ struct console *c;
+ u64 last_diff = 0;
+ u64 printk_seq;
+ u64 diff;
+ u64 seq;
+
+ might_sleep();
+
+ seq = prb_next_seq(prb);
+
+ for (;;) {
+ diff = 0;
+
+ console_lock();
+
+ for_each_console(c) {
+ if (con && con != c)
+ continue;
+ if (!console_is_usable(c))
+ continue;
+ printk_seq = c->seq;
+ if (printk_seq < seq)
+ diff += seq - printk_seq;
+ }
+
+ /*
+ * If consoles are suspended, it cannot be expected that they
+ * make forward progress, so timeout immediately. @diff is
+ * still used to return a valid flush status.
+ */
+ if (console_suspended)
+ remaining = 0;
+ else if (diff != last_diff && reset_on_progress)
+ remaining = timeout_ms;
+
+ console_unlock();
+
+ if (diff == 0 || remaining == 0)
+ break;
+
+ if (remaining < 0) {
+ /* no timeout limit */
+ msleep(100);
+ } else if (remaining < 100) {
+ msleep(remaining);
+ remaining = 0;
+ } else {
+ msleep(100);
+ remaining -= 100;
+ }
+
+ last_diff = diff;
+ }
+
+ return (diff == 0);
+}
+
+/**
+ * pr_flush() - Wait for printing threads to catch up.
+ *
+ * @timeout_ms: The maximum time (in ms) to wait.
+ * @reset_on_progress: Reset the timeout if forward progress is seen.
+ *
+ * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
+ * represents infinite waiting.
+ *
+ * If @reset_on_progress is true, the timeout will be reset whenever any
+ * printer has been seen to make some forward progress.
+ *
+ * Context: Process context. May sleep while acquiring console lock.
+ * Return: true if all enabled printers are caught up.
+ */
+static bool pr_flush(int timeout_ms, bool reset_on_progress)
+{
+ return __pr_flush(NULL, timeout_ms, reset_on_progress);
+}
+
+/*
+ * Delayed printk version, for scheduler-internal messages:
+ */
+#define PRINTK_PENDING_WAKEUP 0x01
+#define PRINTK_PENDING_OUTPUT 0x02
+
+static DEFINE_PER_CPU(int, printk_pending);
+
+static void wake_up_klogd_work_func(struct irq_work *irq_work)
+{
+ int pending = this_cpu_xchg(printk_pending, 0);
+
+ if (pending & PRINTK_PENDING_OUTPUT) {
+ /* If trylock fails, someone else is doing the printing */
+ if (console_trylock())
+ console_unlock();
+ }
+
+ if (pending & PRINTK_PENDING_WAKEUP)
+ wake_up_interruptible(&log_wait);
+}
+
+static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
+ IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
+
+static void __wake_up_klogd(int val)
+{
+ if (!printk_percpu_data_ready())
+ return;
+
+ preempt_disable();
+ /*
+ * Guarantee any new records can be seen by tasks preparing to wait
+ * before this context checks if the wait queue is empty.
+ *
+ * The full memory barrier within wq_has_sleeper() pairs with the full
+ * memory barrier within set_current_state() of
+ * prepare_to_wait_event(), which is called after ___wait_event() adds
+ * the waiter but before it has checked the wait condition.
+ *
+ * This pairs with devkmsg_read:A and syslog_print:A.
+ */
+ if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
+ (val & PRINTK_PENDING_OUTPUT)) {
+ this_cpu_or(printk_pending, val);
+ irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
+ }
+ preempt_enable();
+}
+
+/**
+ * wake_up_klogd - Wake kernel logging daemon
+ *
+ * Use this function when new records have been added to the ringbuffer
+ * and the console printing of those records has already occurred or is
+ * known to be handled by some other context. This function will only
+ * wake the logging daemon.
+ *
+ * Context: Any context.
+ */
+void wake_up_klogd(void)
+{
+ __wake_up_klogd(PRINTK_PENDING_WAKEUP);
+}
+
+/**
+ * defer_console_output - Wake kernel logging daemon and trigger
+ * console printing in a deferred context
+ *
+ * Use this function when new records have been added to the ringbuffer,
+ * this context is responsible for console printing those records, but
+ * the current context is not allowed to perform the console printing.
+ * Trigger an irq_work context to perform the console printing. This
+ * function also wakes the logging daemon.
+ *
+ * Context: Any context.
+ */
+void defer_console_output(void)
+{
+ /*
+ * New messages may have been added directly to the ringbuffer
+ * using vprintk_store(), so wake any waiters as well.
+ */
+ __wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
+}
+
+void printk_trigger_flush(void)
+{
+ defer_console_output();
+}
+
+int vprintk_deferred(const char *fmt, va_list args)
+{
+ return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
+}
+
+int _printk_deferred(const char *fmt, ...)
+{
+ va_list args;
+ int r;
+
+ va_start(args, fmt);
+ r = vprintk_deferred(fmt, args);
+ va_end(args);
+
+ return r;
+}
+
+/*
+ * printk rate limiting, lifted from the networking subsystem.
+ *
+ * This enforces a rate limit: not more than 10 kernel messages
+ * every 5s to make a denial-of-service attack impossible.
+ */
+DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
+
+int __printk_ratelimit(const char *func)
+{
+ return ___ratelimit(&printk_ratelimit_state, func);
+}
+EXPORT_SYMBOL(__printk_ratelimit);
+
+/**
+ * printk_timed_ratelimit - caller-controlled printk ratelimiting
+ * @caller_jiffies: pointer to caller's state
+ * @interval_msecs: minimum interval between prints
+ *
+ * printk_timed_ratelimit() returns true if more than @interval_msecs
+ * milliseconds have elapsed since the last time printk_timed_ratelimit()
+ * returned true.
+ */
+bool printk_timed_ratelimit(unsigned long *caller_jiffies,
+ unsigned int interval_msecs)
+{
+ unsigned long elapsed = jiffies - *caller_jiffies;
+
+ if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
+ return false;
+
+ *caller_jiffies = jiffies;
+ return true;
+}
+EXPORT_SYMBOL(printk_timed_ratelimit);
+
+static DEFINE_SPINLOCK(dump_list_lock);
+static LIST_HEAD(dump_list);
+
+/**
+ * kmsg_dump_register - register a kernel log dumper.
+ * @dumper: pointer to the kmsg_dumper structure
+ *
+ * Adds a kernel log dumper to the system. The dump callback in the
+ * structure will be called when the kernel oopses or panics and must be
+ * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
+ */
+int kmsg_dump_register(struct kmsg_dumper *dumper)
+{
+ unsigned long flags;
+ int err = -EBUSY;
+
+ /* The dump callback needs to be set */
+ if (!dumper->dump)
+ return -EINVAL;
+
+ spin_lock_irqsave(&dump_list_lock, flags);
+ /* Don't allow registering multiple times */
+ if (!dumper->registered) {
+ dumper->registered = 1;
+ list_add_tail_rcu(&dumper->list, &dump_list);
+ err = 0;
+ }
+ spin_unlock_irqrestore(&dump_list_lock, flags);
+
+ return err;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_register);
+
+/**
+ * kmsg_dump_unregister - unregister a kmsg dumper.
+ * @dumper: pointer to the kmsg_dumper structure
+ *
+ * Removes a dump device from the system. Returns zero on success and
+ * %-EINVAL otherwise.
+ */
+int kmsg_dump_unregister(struct kmsg_dumper *dumper)
+{
+ unsigned long flags;
+ int err = -EINVAL;
+
+ spin_lock_irqsave(&dump_list_lock, flags);
+ if (dumper->registered) {
+ dumper->registered = 0;
+ list_del_rcu(&dumper->list);
+ err = 0;
+ }
+ spin_unlock_irqrestore(&dump_list_lock, flags);
+ synchronize_rcu();
+
+ return err;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
+
+static bool always_kmsg_dump;
+module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
+
+const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
+{
+ switch (reason) {
+ case KMSG_DUMP_PANIC:
+ return "Panic";
+ case KMSG_DUMP_OOPS:
+ return "Oops";
+ case KMSG_DUMP_EMERG:
+ return "Emergency";
+ case KMSG_DUMP_SHUTDOWN:
+ return "Shutdown";
+ default:
+ return "Unknown";
+ }
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
+
+/**
+ * kmsg_dump - dump kernel log to kernel message dumpers.
+ * @reason: the reason (oops, panic etc) for dumping
+ *
+ * Call each of the registered dumper's dump() callback, which can
+ * retrieve the kmsg records with kmsg_dump_get_line() or
+ * kmsg_dump_get_buffer().
+ */
+void kmsg_dump(enum kmsg_dump_reason reason)
+{
+ struct kmsg_dumper *dumper;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(dumper, &dump_list, list) {
+ enum kmsg_dump_reason max_reason = dumper->max_reason;
+
+ /*
+ * If client has not provided a specific max_reason, default
+ * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
+ */
+ if (max_reason == KMSG_DUMP_UNDEF) {
+ max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
+ KMSG_DUMP_OOPS;
+ }
+ if (reason > max_reason)
+ continue;
+
+ /* invoke dumper which will iterate over records */
+ dumper->dump(dumper, reason);
+ }
+ rcu_read_unlock();
+}
+
+/**
+ * kmsg_dump_get_line - retrieve one kmsg log line
+ * @iter: kmsg dump iterator
+ * @syslog: include the "<4>" prefixes
+ * @line: buffer to copy the line to
+ * @size: maximum size of the buffer
+ * @len: length of line placed into buffer
+ *
+ * Start at the beginning of the kmsg buffer, with the oldest kmsg
+ * record, and copy one record into the provided buffer.
+ *
+ * Consecutive calls will return the next available record moving
+ * towards the end of the buffer with the youngest messages.
+ *
+ * A return value of FALSE indicates that there are no more records to
+ * read.
+ */
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
+ char *line, size_t size, size_t *len)
+{
+ u64 min_seq = latched_seq_read_nolock(&clear_seq);
+ struct printk_info info;
+ unsigned int line_count;
+ struct printk_record r;
+ size_t l = 0;
+ bool ret = false;
+
+ if (iter->cur_seq < min_seq)
+ iter->cur_seq = min_seq;
+
+ prb_rec_init_rd(&r, &info, line, size);
+
+ /* Read text or count text lines? */
+ if (line) {
+ if (!prb_read_valid(prb, iter->cur_seq, &r))
+ goto out;
+ l = record_print_text(&r, syslog, printk_time);
+ } else {
+ if (!prb_read_valid_info(prb, iter->cur_seq,
+ &info, &line_count)) {
+ goto out;
+ }
+ l = get_record_print_text_size(&info, line_count, syslog,
+ printk_time);
+
+ }
+
+ iter->cur_seq = r.info->seq + 1;
+ ret = true;
+out:
+ if (len)
+ *len = l;
+ return ret;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
+
+/**
+ * kmsg_dump_get_buffer - copy kmsg log lines
+ * @iter: kmsg dump iterator
+ * @syslog: include the "<4>" prefixes
+ * @buf: buffer to copy the line to
+ * @size: maximum size of the buffer
+ * @len_out: length of line placed into buffer
+ *
+ * Start at the end of the kmsg buffer and fill the provided buffer
+ * with as many of the *youngest* kmsg records that fit into it.
+ * If the buffer is large enough, all available kmsg records will be
+ * copied with a single call.
+ *
+ * Consecutive calls will fill the buffer with the next block of
+ * available older records, not including the earlier retrieved ones.
+ *
+ * A return value of FALSE indicates that there are no more records to
+ * read.
+ */
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
+ char *buf, size_t size, size_t *len_out)
+{
+ u64 min_seq = latched_seq_read_nolock(&clear_seq);
+ struct printk_info info;
+ struct printk_record r;
+ u64 seq;
+ u64 next_seq;
+ size_t len = 0;
+ bool ret = false;
+ bool time = printk_time;
+
+ if (!buf || !size)
+ goto out;
+
+ if (iter->cur_seq < min_seq)
+ iter->cur_seq = min_seq;
+
+ if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
+ if (info.seq != iter->cur_seq) {
+ /* messages are gone, move to first available one */
+ iter->cur_seq = info.seq;
+ }
+ }
+
+ /* last entry */
+ if (iter->cur_seq >= iter->next_seq)
+ goto out;
+
+ /*
+ * Find first record that fits, including all following records,
+ * into the user-provided buffer for this dump. Pass in size-1
+ * because this function (by way of record_print_text()) will
+ * not write more than size-1 bytes of text into @buf.
+ */
+ seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
+ size - 1, syslog, time);
+
+ /*
+ * Next kmsg_dump_get_buffer() invocation will dump block of
+ * older records stored right before this one.
+ */
+ next_seq = seq;
+
+ prb_rec_init_rd(&r, &info, buf, size);
+
+ len = 0;
+ prb_for_each_record(seq, prb, seq, &r) {
+ if (r.info->seq >= iter->next_seq)
+ break;
+
+ len += record_print_text(&r, syslog, time);
+
+ /* Adjust record to store to remaining buffer space. */
+ prb_rec_init_rd(&r, &info, buf + len, size - len);
+ }
+
+ iter->next_seq = next_seq;
+ ret = true;
+out:
+ if (len_out)
+ *len_out = len;
+ return ret;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
+
+/**
+ * kmsg_dump_rewind - reset the iterator
+ * @iter: kmsg dump iterator
+ *
+ * Reset the dumper's iterator so that kmsg_dump_get_line() and
+ * kmsg_dump_get_buffer() can be called again and used multiple
+ * times within the same dumper.dump() callback.
+ */
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
+{
+ iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+ iter->next_seq = prb_next_seq(prb);
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
+
+#endif
+
+#ifdef CONFIG_SMP
+static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
+static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
+
+/**
+ * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
+ * spinning lock is not owned by any CPU.
+ *
+ * Context: Any context.
+ */
+void __printk_cpu_sync_wait(void)
+{
+ do {
+ cpu_relax();
+ } while (atomic_read(&printk_cpu_sync_owner) != -1);
+}
+EXPORT_SYMBOL(__printk_cpu_sync_wait);
+
+/**
+ * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
+ * spinning lock.
+ *
+ * If no processor has the lock, the calling processor takes the lock and
+ * becomes the owner. If the calling processor is already the owner of the
+ * lock, this function succeeds immediately.
+ *
+ * Context: Any context. Expects interrupts to be disabled.
+ * Return: 1 on success, otherwise 0.
+ */
+int __printk_cpu_sync_try_get(void)
+{
+ int cpu;
+ int old;
+
+ cpu = smp_processor_id();
+
+ /*
+ * Guarantee loads and stores from this CPU when it is the lock owner
+ * are _not_ visible to the previous lock owner. This pairs with
+ * __printk_cpu_sync_put:B.
+ *
+ * Memory barrier involvement:
+ *
+ * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
+ * then __printk_cpu_sync_put:A can never read from
+ * __printk_cpu_sync_try_get:B.
+ *
+ * Relies on:
+ *
+ * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
+ * of the previous CPU
+ * matching
+ * ACQUIRE from __printk_cpu_sync_try_get:A to
+ * __printk_cpu_sync_try_get:B of this CPU
+ */
+ old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
+ cpu); /* LMM(__printk_cpu_sync_try_get:A) */
+ if (old == -1) {
+ /*
+ * This CPU is now the owner and begins loading/storing
+ * data: LMM(__printk_cpu_sync_try_get:B)
+ */
+ return 1;
+
+ } else if (old == cpu) {
+ /* This CPU is already the owner. */
+ atomic_inc(&printk_cpu_sync_nested);
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(__printk_cpu_sync_try_get);
+
+/**
+ * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
+ *
+ * The calling processor must be the owner of the lock.
+ *
+ * Context: Any context. Expects interrupts to be disabled.
+ */
+void __printk_cpu_sync_put(void)
+{
+ if (atomic_read(&printk_cpu_sync_nested)) {
+ atomic_dec(&printk_cpu_sync_nested);
+ return;
+ }
+
+ /*
+ * This CPU is finished loading/storing data:
+ * LMM(__printk_cpu_sync_put:A)
+ */
+
+ /*
+ * Guarantee loads and stores from this CPU when it was the
+ * lock owner are visible to the next lock owner. This pairs
+ * with __printk_cpu_sync_try_get:A.
+ *
+ * Memory barrier involvement:
+ *
+ * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
+ * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
+ *
+ * Relies on:
+ *
+ * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
+ * of this CPU
+ * matching
+ * ACQUIRE from __printk_cpu_sync_try_get:A to
+ * __printk_cpu_sync_try_get:B of the next CPU
+ */
+ atomic_set_release(&printk_cpu_sync_owner,
+ -1); /* LMM(__printk_cpu_sync_put:B) */
+}
+EXPORT_SYMBOL(__printk_cpu_sync_put);
+#endif /* CONFIG_SMP */