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perf: Simplify child event tear-down

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lkml.kernel.org/r/20250307193305.486326750@infradead.org
This commit is contained in:
Peter Zijlstra
2025-01-17 15:25:23 +01:00
parent 7ed9138a72
commit 0a00a43b8c
1 changed files with 6 additions and 2 deletions
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8
kernel/events/core.c
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@@ -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 @@ again:
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;
}