The following commit has been merged into the perf/core branch of tip:
Commit-ID: 0a00a43b8c200df5b9ca2b3e1726479b5916264b
Gitweb: https://git.kernel.org/tip/0a00a43b8c200df5b9ca2b3e1726479b5916264b
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 17 Jan 2025 15:25:23 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Apr 2025 20:55:46 +02:00
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: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lkml.kernel.org/r/20250307193305.486326750@infradead.org
---
kernel/events/core.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a85d63b..3c92b75 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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;
}