Commit 8eaec7bb authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarRavi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20241104135519.463607258@infradead.org
parent 0c8a4e41

kernel/events/core.c

+15 −10
Original line number Diff line number Diff line
@@ -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;

			}



			/*

			 * 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