6.6-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
commit 2ab9d830262c132ab5db2f571003d80850d56b2a upstream.
Ole reported that event->mmap_mutex is strictly insufficient to serialize the AUX buffer, add a per RB mutex to fully serialize it.
Note that in the lock order comment the perf_event::mmap_mutex order was already wrong, that is, it nesting under mmap_lock is not new with this patch.
Fixes: 45bfb2e50471 ("perf: Add AUX area to ring buffer for raw data streams") Reported-by: Ole ole@binarygecko.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/events/core.c | 18 ++++++++++++------ kernel/events/internal.h | 1 + kernel/events/ring_buffer.c | 2 ++ 3 files changed, 15 insertions(+), 6 deletions(-)
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1255,8 +1255,9 @@ static void put_ctx(struct perf_event_co * perf_event_context::mutex * perf_event::child_mutex; * perf_event_context::lock - * perf_event::mmap_mutex * mmap_lock + * perf_event::mmap_mutex + * perf_buffer::aux_mutex * perf_addr_filters_head::lock * * cpu_hotplug_lock @@ -6352,12 +6353,11 @@ static void perf_mmap_close(struct vm_ar event->pmu->event_unmapped(event, vma->vm_mm);
/* - * rb->aux_mmap_count will always drop before rb->mmap_count and - * event->mmap_count, so it is ok to use event->mmap_mutex to - * serialize with perf_mmap here. + * The AUX buffer is strictly a sub-buffer, serialize using aux_mutex + * to avoid complications. */ if (rb_has_aux(rb) && vma->vm_pgoff == rb->aux_pgoff && - atomic_dec_and_mutex_lock(&rb->aux_mmap_count, &event->mmap_mutex)) { + atomic_dec_and_mutex_lock(&rb->aux_mmap_count, &rb->aux_mutex)) { /* * Stop all AUX events that are writing to this buffer, * so that we can free its AUX pages and corresponding PMU @@ -6374,7 +6374,7 @@ static void perf_mmap_close(struct vm_ar rb_free_aux(rb); WARN_ON_ONCE(refcount_read(&rb->aux_refcount));
- mutex_unlock(&event->mmap_mutex); + mutex_unlock(&rb->aux_mutex); }
if (atomic_dec_and_test(&rb->mmap_count)) @@ -6462,6 +6462,7 @@ static int perf_mmap(struct file *file, struct perf_event *event = file->private_data; unsigned long user_locked, user_lock_limit; struct user_struct *user = current_user(); + struct mutex *aux_mutex = NULL; struct perf_buffer *rb = NULL; unsigned long locked, lock_limit; unsigned long vma_size; @@ -6510,6 +6511,9 @@ static int perf_mmap(struct file *file, if (!rb) goto aux_unlock;
+ aux_mutex = &rb->aux_mutex; + mutex_lock(aux_mutex); + aux_offset = READ_ONCE(rb->user_page->aux_offset); aux_size = READ_ONCE(rb->user_page->aux_size);
@@ -6660,6 +6664,8 @@ unlock: atomic_dec(&rb->mmap_count); } aux_unlock: + if (aux_mutex) + mutex_unlock(aux_mutex); mutex_unlock(&event->mmap_mutex);
/* --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -40,6 +40,7 @@ struct perf_buffer { struct user_struct *mmap_user;
/* AUX area */ + struct mutex aux_mutex; long aux_head; unsigned int aux_nest; long aux_wakeup; /* last aux_watermark boundary crossed by aux_head */ --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -333,6 +333,8 @@ ring_buffer_init(struct perf_buffer *rb, */ if (!rb->nr_pages) rb->paused = 1; + + mutex_init(&rb->aux_mutex); }
void perf_aux_output_flag(struct perf_output_handle *handle, u64 flags)