Adding upstream version 6.10.3.upstream/6.10.3

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

1 files changed, 463 insertions, 24 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 54887f4c35..28853966aa 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -9,6 +9,7 @@
 #include <linux/ring_buffer.h>
 #include <linux/trace_clock.h>
 #include <linux/sched/clock.h>
+#include <linux/cacheflush.h>
 #include <linux/trace_seq.h>
 #include <linux/spinlock.h>
 #include <linux/irq_work.h>
@@ -26,6 +27,7 @@
 #include <linux/list.h>
 #include <linux/cpu.h>
 #include <linux/oom.h>
+#include <linux/mm.h>
 
 #include <asm/local64.h>
 #include <asm/local.h>
@@ -312,6 +314,8 @@ static u64 rb_event_time_stamp(struct ring_buffer_event *event)
 /* Missed count stored at end */
 #define RB_MISSED_STORED	(1 << 30)
 
+#define RB_MISSED_MASK		(3 << 30)
+
 struct buffer_data_page {
 	u64		 time_stamp;	/* page time stamp */
 	local_t		 commit;	/* write committed index */
@@ -338,6 +342,7 @@ struct buffer_page {
 	local_t		 entries;	/* entries on this page */
 	unsigned long	 real_end;	/* real end of data */
 	unsigned	 order;		/* order of the page */
+	u32		 id;		/* ID for external mapping */
 	struct buffer_data_page *page;	/* Actual data page */
 };
 
@@ -484,6 +489,12 @@ struct ring_buffer_per_cpu {
 	u64				read_stamp;
 	/* pages removed since last reset */
 	unsigned long			pages_removed;
+
+	unsigned int			mapped;
+	struct mutex			mapping_lock;
+	unsigned long			*subbuf_ids;	/* ID to subbuf VA */
+	struct trace_buffer_meta	*meta_page;
+
 	/* ring buffer pages to update, > 0 to add, < 0 to remove */
 	long				nr_pages_to_update;
 	struct list_head		new_pages; /* new pages to add */
@@ -1529,7 +1540,7 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 		list_add(&bpage->list, pages);
 
 		page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu),
-					mflags | __GFP_ZERO,
+					mflags | __GFP_COMP | __GFP_ZERO,
 					cpu_buffer->buffer->subbuf_order);
 		if (!page)
 			goto free_pages;
@@ -1604,6 +1615,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 	init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
 	init_waitqueue_head(&cpu_buffer->irq_work.waiters);
 	init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
+	mutex_init(&cpu_buffer->mapping_lock);
 
 	bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
 			    GFP_KERNEL, cpu_to_node(cpu));
@@ -1614,7 +1626,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 
 	cpu_buffer->reader_page = bpage;
 
-	page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_ZERO,
+	page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_COMP | __GFP_ZERO,
 				cpu_buffer->buffer->subbuf_order);
 	if (!page)
 		goto fail_free_reader;
@@ -1794,8 +1806,6 @@ bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
 	return buffer->time_stamp_abs;
 }
 
-static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
-
 static inline unsigned long rb_page_entries(struct buffer_page *bpage)
 {
 	return local_read(&bpage->entries) & RB_WRITE_MASK;
@@ -2327,7 +2337,7 @@ rb_iter_head_event(struct ring_buffer_iter *iter)
 /* Size is determined by what has been committed */
 static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
 {
-	return rb_page_commit(bpage);
+	return rb_page_commit(bpage) & ~RB_MISSED_MASK;
 }
 
 static __always_inline unsigned
@@ -3954,7 +3964,7 @@ static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
 		return true;
 
 	/* Reader should exhaust content in reader page */
-	if (reader->read != rb_page_commit(reader))
+	if (reader->read != rb_page_size(reader))
 		return false;
 
 	/*
@@ -4425,7 +4435,7 @@ int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
 	return ((iter->head_page == commit_page && iter->head >= commit) ||
 		(iter->head_page == reader && commit_page == head_page &&
 		 head_page->read == commit &&
-		 iter->head == rb_page_commit(cpu_buffer->reader_page)));
+		 iter->head == rb_page_size(cpu_buffer->reader_page)));
 }
 EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
 
@@ -5045,13 +5055,9 @@ EXPORT_SYMBOL_GPL(ring_buffer_consume);
  * @flags: gfp flags to use for memory allocation
  *
  * This performs the initial preparations necessary to iterate
- * through the buffer.  Memory is allocated, buffer recording
+ * through the buffer.  Memory is allocated, buffer resizing
  * is disabled, and the iterator pointer is returned to the caller.
  *
- * Disabling buffer recording prevents the reading from being
- * corrupted. This is not a consuming read, so a producer is not
- * expected.
- *
  * After a sequence of ring_buffer_read_prepare calls, the user is
  * expected to make at least one call to ring_buffer_read_prepare_sync.
  * Afterwards, ring_buffer_read_start is invoked to get things going
@@ -5138,8 +5144,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_read_start);
  * ring_buffer_read_finish - finish reading the iterator of the buffer
  * @iter: The iterator retrieved by ring_buffer_start
  *
- * This re-enables the recording to the buffer, and frees the
- * iterator.
+ * This re-enables resizing of the buffer, and frees the iterator.
  */
 void
 ring_buffer_read_finish(struct ring_buffer_iter *iter)
@@ -5147,12 +5152,7 @@ ring_buffer_read_finish(struct ring_buffer_iter *iter)
 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
 	unsigned long flags;
 
-	/*
-	 * Ring buffer is disabled from recording, here's a good place
-	 * to check the integrity of the ring buffer.
-	 * Must prevent readers from trying to read, as the check
-	 * clears the HEAD page and readers require it.
-	 */
+	/* Use this opportunity to check the integrity of the ring buffer. */
 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 	rb_check_pages(cpu_buffer);
 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
@@ -5220,6 +5220,22 @@ static void rb_clear_buffer_page(struct buffer_page *page)
 	page->read = 0;
 }
 
+static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
+
+	meta->reader.read = cpu_buffer->reader_page->read;
+	meta->reader.id = cpu_buffer->reader_page->id;
+	meta->reader.lost_events = cpu_buffer->lost_events;
+
+	meta->entries = local_read(&cpu_buffer->entries);
+	meta->overrun = local_read(&cpu_buffer->overrun);
+	meta->read = cpu_buffer->read;
+
+	/* Some archs do not have data cache coherency between kernel and user-space */
+	flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page));
+}
+
 static void
 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 {
@@ -5264,6 +5280,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 	cpu_buffer->lost_events = 0;
 	cpu_buffer->last_overrun = 0;
 
+	if (cpu_buffer->mapped)
+		rb_update_meta_page(cpu_buffer);
+
 	rb_head_page_activate(cpu_buffer);
 	cpu_buffer->pages_removed = 0;
 }
@@ -5478,6 +5497,12 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
 	cpu_buffer_a = buffer_a->buffers[cpu];
 	cpu_buffer_b = buffer_b->buffers[cpu];
 
+	/* It's up to the callers to not try to swap mapped buffers */
+	if (WARN_ON_ONCE(cpu_buffer_a->mapped || cpu_buffer_b->mapped)) {
+		ret = -EBUSY;
+		goto out;
+	}
+
 	/* At least make sure the two buffers are somewhat the same */
 	if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
 		goto out;
@@ -5588,7 +5613,7 @@ ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
 		goto out;
 
 	page = alloc_pages_node(cpu_to_node(cpu),
-				GFP_KERNEL | __GFP_NORETRY | __GFP_ZERO,
+				GFP_KERNEL | __GFP_NORETRY | __GFP_COMP | __GFP_ZERO,
 				cpu_buffer->buffer->subbuf_order);
 	if (!page) {
 		kfree(bpage);
@@ -5729,7 +5754,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	event = rb_reader_event(cpu_buffer);
 
 	read = reader->read;
-	commit = rb_page_commit(reader);
+	commit = rb_page_size(reader);
 
 	/* Check if any events were dropped */
 	missed_events = cpu_buffer->lost_events;
@@ -5742,7 +5767,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	 * Otherwise, we can simply swap the page with the one passed in.
 	 */
 	if (read || (len < (commit - read)) ||
-	    cpu_buffer->reader_page == cpu_buffer->commit_page) {
+	    cpu_buffer->reader_page == cpu_buffer->commit_page ||
+	    cpu_buffer->mapped) {
 		struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
 		unsigned int rpos = read;
 		unsigned int pos = 0;
@@ -5805,7 +5831,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	} else {
 		/* update the entry counter */
 		cpu_buffer->read += rb_page_entries(reader);
-		cpu_buffer->read_bytes += rb_page_commit(reader);
+		cpu_buffer->read_bytes += rb_page_size(reader);
 
 		/* swap the pages */
 		rb_init_page(bpage);
@@ -5965,6 +5991,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 
 		cpu_buffer = buffer->buffers[cpu];
 
+		if (cpu_buffer->mapped) {
+			err = -EBUSY;
+			goto error;
+		}
+
 		/* Update the number of pages to match the new size */
 		nr_pages = old_size * buffer->buffers[cpu]->nr_pages;
 		nr_pages = DIV_ROUND_UP(nr_pages, buffer->subbuf_size);
@@ -6066,6 +6097,414 @@ error:
 }
 EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
 
+static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct page *page;
+
+	if (cpu_buffer->meta_page)
+		return 0;
+
+	page = alloc_page(GFP_USER | __GFP_ZERO);
+	if (!page)
+		return -ENOMEM;
+
+	cpu_buffer->meta_page = page_to_virt(page);
+
+	return 0;
+}
+
+static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	unsigned long addr = (unsigned long)cpu_buffer->meta_page;
+
+	free_page(addr);
+	cpu_buffer->meta_page = NULL;
+}
+
+static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
+				   unsigned long *subbuf_ids)
+{
+	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
+	unsigned int nr_subbufs = cpu_buffer->nr_pages + 1;
+	struct buffer_page *first_subbuf, *subbuf;
+	int id = 0;
+
+	subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page;
+	cpu_buffer->reader_page->id = id++;
+
+	first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
+	do {
+		if (WARN_ON(id >= nr_subbufs))
+			break;
+
+		subbuf_ids[id] = (unsigned long)subbuf->page;
+		subbuf->id = id;
+
+		rb_inc_page(&subbuf);
+		id++;
+	} while (subbuf != first_subbuf);
+
+	/* install subbuf ID to kern VA translation */
+	cpu_buffer->subbuf_ids = subbuf_ids;
+
+	meta->meta_page_size = PAGE_SIZE;
+	meta->meta_struct_len = sizeof(*meta);
+	meta->nr_subbufs = nr_subbufs;
+	meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE;
+
+	rb_update_meta_page(cpu_buffer);
+}
+
+static struct ring_buffer_per_cpu *
+rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return ERR_PTR(-EINVAL);
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	mutex_lock(&cpu_buffer->mapping_lock);
+
+	if (!cpu_buffer->mapped) {
+		mutex_unlock(&cpu_buffer->mapping_lock);
+		return ERR_PTR(-ENODEV);
+	}
+
+	return cpu_buffer;
+}
+
+static void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	mutex_unlock(&cpu_buffer->mapping_lock);
+}
+
+/*
+ * Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need
+ * to be set-up or torn-down.
+ */
+static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,
+			       bool inc)
+{
+	unsigned long flags;
+
+	lockdep_assert_held(&cpu_buffer->mapping_lock);
+
+	if (inc && cpu_buffer->mapped == UINT_MAX)
+		return -EBUSY;
+
+	if (WARN_ON(!inc && cpu_buffer->mapped == 0))
+		return -EINVAL;
+
+	mutex_lock(&cpu_buffer->buffer->mutex);
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	if (inc)
+		cpu_buffer->mapped++;
+	else
+		cpu_buffer->mapped--;
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	mutex_unlock(&cpu_buffer->buffer->mutex);
+
+	return 0;
+}
+
+/*
+ *   +--------------+  pgoff == 0
+ *   |   meta page  |
+ *   +--------------+  pgoff == 1
+ *   | subbuffer 0  |
+ *   |              |
+ *   +--------------+  pgoff == (1 + (1 << subbuf_order))
+ *   | subbuffer 1  |
+ *   |              |
+ *         ...
+ */
+#ifdef CONFIG_MMU
+static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
+			struct vm_area_struct *vma)
+{
+	unsigned long nr_subbufs, nr_pages, vma_pages, pgoff = vma->vm_pgoff;
+	unsigned int subbuf_pages, subbuf_order;
+	struct page **pages;
+	int p = 0, s = 0;
+	int err;
+
+	/* Refuse MP_PRIVATE or writable mappings */
+	if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC ||
+	    !(vma->vm_flags & VM_MAYSHARE))
+		return -EPERM;
+
+	/*
+	 * Make sure the mapping cannot become writable later. Also tell the VM
+	 * to not touch these pages (VM_DONTCOPY | VM_DONTEXPAND).
+	 */
+	vm_flags_mod(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP,
+		     VM_MAYWRITE);
+
+	lockdep_assert_held(&cpu_buffer->mapping_lock);
+
+	subbuf_order = cpu_buffer->buffer->subbuf_order;
+	subbuf_pages = 1 << subbuf_order;
+
+	nr_subbufs = cpu_buffer->nr_pages + 1; /* + reader-subbuf */
+	nr_pages = ((nr_subbufs) << subbuf_order) - pgoff + 1; /* + meta-page */
+
+	vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	if (!vma_pages || vma_pages > nr_pages)
+		return -EINVAL;
+
+	nr_pages = vma_pages;
+
+	pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL);
+	if (!pages)
+		return -ENOMEM;
+
+	if (!pgoff) {
+		pages[p++] = virt_to_page(cpu_buffer->meta_page);
+
+		/*
+		 * TODO: Align sub-buffers on their size, once
+		 * vm_insert_pages() supports the zero-page.
+		 */
+	} else {
+		/* Skip the meta-page */
+		pgoff--;
+
+		if (pgoff % subbuf_pages) {
+			err = -EINVAL;
+			goto out;
+		}
+
+		s += pgoff / subbuf_pages;
+	}
+
+	while (p < nr_pages) {
+		struct page *page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]);
+		int off = 0;
+
+		if (WARN_ON_ONCE(s >= nr_subbufs)) {
+			err = -EINVAL;
+			goto out;
+		}
+
+		for (; off < (1 << (subbuf_order)); off++, page++) {
+			if (p >= nr_pages)
+				break;
+
+			pages[p++] = page;
+		}
+		s++;
+	}
+
+	err = vm_insert_pages(vma, vma->vm_start, pages, &nr_pages);
+
+out:
+	kfree(pages);
+
+	return err;
+}
+#else
+static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
+			struct vm_area_struct *vma)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
+int ring_buffer_map(struct trace_buffer *buffer, int cpu,
+		    struct vm_area_struct *vma)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags, *subbuf_ids;
+	int err = 0;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return -EINVAL;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	mutex_lock(&cpu_buffer->mapping_lock);
+
+	if (cpu_buffer->mapped) {
+		err = __rb_map_vma(cpu_buffer, vma);
+		if (!err)
+			err = __rb_inc_dec_mapped(cpu_buffer, true);
+		mutex_unlock(&cpu_buffer->mapping_lock);
+		return err;
+	}
+
+	/* prevent another thread from changing buffer/sub-buffer sizes */
+	mutex_lock(&buffer->mutex);
+
+	err = rb_alloc_meta_page(cpu_buffer);
+	if (err)
+		goto unlock;
+
+	/* subbuf_ids include the reader while nr_pages does not */
+	subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL);
+	if (!subbuf_ids) {
+		rb_free_meta_page(cpu_buffer);
+		err = -ENOMEM;
+		goto unlock;
+	}
+
+	atomic_inc(&cpu_buffer->resize_disabled);
+
+	/*
+	 * Lock all readers to block any subbuf swap until the subbuf IDs are
+	 * assigned.
+	 */
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+	rb_setup_ids_meta_page(cpu_buffer, subbuf_ids);
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+	err = __rb_map_vma(cpu_buffer, vma);
+	if (!err) {
+		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+		cpu_buffer->mapped = 1;
+		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	} else {
+		kfree(cpu_buffer->subbuf_ids);
+		cpu_buffer->subbuf_ids = NULL;
+		rb_free_meta_page(cpu_buffer);
+	}
+
+unlock:
+	mutex_unlock(&buffer->mutex);
+	mutex_unlock(&cpu_buffer->mapping_lock);
+
+	return err;
+}
+
+int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags;
+	int err = 0;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return -EINVAL;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	mutex_lock(&cpu_buffer->mapping_lock);
+
+	if (!cpu_buffer->mapped) {
+		err = -ENODEV;
+		goto out;
+	} else if (cpu_buffer->mapped > 1) {
+		__rb_inc_dec_mapped(cpu_buffer, false);
+		goto out;
+	}
+
+	mutex_lock(&buffer->mutex);
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	cpu_buffer->mapped = 0;
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+	kfree(cpu_buffer->subbuf_ids);
+	cpu_buffer->subbuf_ids = NULL;
+	rb_free_meta_page(cpu_buffer);
+	atomic_dec(&cpu_buffer->resize_disabled);
+
+	mutex_unlock(&buffer->mutex);
+
+out:
+	mutex_unlock(&cpu_buffer->mapping_lock);
+
+	return err;
+}
+
+int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct buffer_page *reader;
+	unsigned long missed_events;
+	unsigned long reader_size;
+	unsigned long flags;
+
+	cpu_buffer = rb_get_mapped_buffer(buffer, cpu);
+	if (IS_ERR(cpu_buffer))
+		return (int)PTR_ERR(cpu_buffer);
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+consume:
+	if (rb_per_cpu_empty(cpu_buffer))
+		goto out;
+
+	reader_size = rb_page_size(cpu_buffer->reader_page);
+
+	/*
+	 * There are data to be read on the current reader page, we can
+	 * return to the caller. But before that, we assume the latter will read
+	 * everything. Let's update the kernel reader accordingly.
+	 */
+	if (cpu_buffer->reader_page->read < reader_size) {
+		while (cpu_buffer->reader_page->read < reader_size)
+			rb_advance_reader(cpu_buffer);
+		goto out;
+	}
+
+	reader = rb_get_reader_page(cpu_buffer);
+	if (WARN_ON(!reader))
+		goto out;
+
+	/* Check if any events were dropped */
+	missed_events = cpu_buffer->lost_events;
+
+	if (cpu_buffer->reader_page != cpu_buffer->commit_page) {
+		if (missed_events) {
+			struct buffer_data_page *bpage = reader->page;
+			unsigned int commit;
+			/*
+			 * Use the real_end for the data size,
+			 * This gives us a chance to store the lost events
+			 * on the page.
+			 */
+			if (reader->real_end)
+				local_set(&bpage->commit, reader->real_end);
+			/*
+			 * If there is room at the end of the page to save the
+			 * missed events, then record it there.
+			 */
+			commit = rb_page_size(reader);
+			if (buffer->subbuf_size - commit >= sizeof(missed_events)) {
+				memcpy(&bpage->data[commit], &missed_events,
+				       sizeof(missed_events));
+				local_add(RB_MISSED_STORED, &bpage->commit);
+			}
+			local_add(RB_MISSED_EVENTS, &bpage->commit);
+		}
+	} else {
+		/*
+		 * There really shouldn't be any missed events if the commit
+		 * is on the reader page.
+		 */
+		WARN_ON_ONCE(missed_events);
+	}
+
+	cpu_buffer->lost_events = 0;
+
+	goto consume;
+
+out:
+	/* Some archs do not have data cache coherency between kernel and user-space */
+	flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page));
+
+	rb_update_meta_page(cpu_buffer);
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	rb_put_mapped_buffer(cpu_buffer);
+
+	return 0;
+}
+
 /*
  * We only allocate new buffers, never free them if the CPU goes down.
  * If we were to free the buffer, then the user would lose any trace that was in