The following commit has been merged into the perf/core branch of tip: Commit-ID: 6cbfc06a8590ab4db69f8af9431e816c859e2776 Gitweb: https://git.kernel.org/tip/6cbfc06a8590ab4db69f8af9431e816c859e2776 Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Mon, 04 Nov 2024 14:39:26 +01:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Sat, 01 Mar 2025 20:25:57 +01:00 perf/core: Remove retry loop from perf_mmap() AFAICT there is no actual benefit from the mutex drop on re-try. The 'worst' case scenario is that we instantly re-gain the mutex without perf_mmap_close() getting it. So might as well make that the normal case. Reflow the code to make the ring buffer detach case naturally flow into the no ring buffer case. [ mingo: Forward ported it ] Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Link: https://lore.kernel.org/r/20241104135519.463607258@xxxxxxxxxxxxx --- kernel/events/core.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 4cd3494..ca4c124 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6719,28 +6719,33 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) return -EINVAL; WARN_ON_ONCE(event->ctx->parent_ctx); -again: mutex_lock(&event->mmap_mutex); + if (event->rb) { if (data_page_nr(event->rb) != nr_pages) { ret = -EINVAL; goto unlock; } - if (!atomic_inc_not_zero(&event->rb->mmap_count)) { + if (atomic_inc_not_zero(&event->rb->mmap_count)) { /* - * Raced against perf_mmap_close(); remove the - * event and try again. + * Success -- managed to mmap() the same buffer + * multiple times. */ - ring_buffer_attach(event, NULL); - mutex_unlock(&event->mmap_mutex); - goto again; + ret = 0; + /* We need the rb to map pages. */ + rb = event->rb; + goto unlock; } - /* We need the rb to map pages. */ - rb = event->rb; - goto unlock; + /* + * Raced against perf_mmap_close()'s + * atomic_dec_and_mutex_lock() remove the + * event and continue as if !event->rb + */ + ring_buffer_attach(event, NULL); } + } else { /* * AUX area mapping: if rb->aux_nr_pages != 0, it's already
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