The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y git checkout FETCH_HEAD git cherry-pick -x 2ab9d830262c132ab5db2f571003d80850d56b2a # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024090922-directed-majorette-f8ad@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

2ab9d830262c ("perf/aux: Fix AUX buffer serialization") c1e8d7c6a7a6 ("mmap locking API: convert mmap_sem comments") d8ed45c5dcd4 ("mmap locking API: use coccinelle to convert mmap_sem rwsem call sites") 5a36f0f3f518 ("Merge tag 'vfio-v5.8-rc1' of git://github.com/awilliam/linux-vfio")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2ab9d830262c132ab5db2f571003d80850d56b2a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra peterz@infradead.org Date: Mon, 2 Sep 2024 10:14:24 +0200 Subject: [PATCH] perf/aux: Fix AUX buffer serialization

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

diff --git a/kernel/events/core.c b/kernel/events/core.c index c973e3c11e03..8a6c6bbcd658 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1255,8 +1255,9 @@ static void put_ctx(struct perf_event_context *ctx) * 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 @@ -6373,12 +6374,11 @@ static void perf_mmap_close(struct vm_area_struct *vma) 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 @@ -6395,7 +6395,7 @@ static void perf_mmap_close(struct vm_area_struct *vma) 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)) @@ -6483,6 +6483,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) 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; @@ -6531,6 +6532,9 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) 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);

@@ -6681,6 +6685,8 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) atomic_dec(&rb->mmap_count); } aux_unlock: + if (aux_mutex) + mutex_unlock(aux_mutex); mutex_unlock(&event->mmap_mutex);

/* diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 451514442a1b..e072d995d670 100644 --- 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 */ diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 8cadf97bc290..4f46f688d0d4 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -337,6 +337,8 @@ ring_buffer_init(struct perf_buffer *rb, long watermark, int flags) */ if (!rb->nr_pages) rb->paused = 1; + + mutex_init(&rb->aux_mutex); }

void perf_aux_output_flag(struct perf_output_handle *handle, u64 flags)