Commit 0a00a43b authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

perf: Simplify child event tear-down 



Currently perf_event_release_kernel() will iterate the child events and attempt
tear-down. However, it removes them from the child_list using list_move(),
notably skipping the state management done by perf_child_detach().

Crucially, it fails to clear PERF_ATTACH_CHILD, which opens the door for a
concurrent perf_remove_from_context() to race.

This way child_list management stays fully serialized using child_mutex.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarRavi Bangoria <ravi.bangoria@amd.com>
Link: https://lkml.kernel.org/r/20250307193305.486326750@infradead.org
parent 7ed9138a

kernel/events/core.c

+6 −2
Original line number Diff line number Diff line
@@ -2325,7 +2325,11 @@ static void perf_child_detach(struct perf_event *event) 
	if (WARN_ON_ONCE(!parent_event))

		return;



	/*

	 * Can't check this from an IPI, the holder is likey another CPU.

	 *

	lockdep_assert_held(&parent_event->child_mutex);

	 */



	sync_child_event(event);

	list_del_init(&event->child_list);
@@ -5759,8 +5763,8 @@ int perf_event_release_kernel(struct perf_event *event) 
		tmp = list_first_entry_or_null(&event->child_list,

					       struct perf_event, child_list);

		if (tmp == child) {

			perf_remove_from_context(child, DETACH_GROUP);

			list_move(&child->child_list, &free_list);

			perf_remove_from_context(child, DETACH_GROUP | DETACH_CHILD);

			list_add(&child->child_list, &free_list);

		} else {

			var = &ctx->refcount;

		}