[tip: perf/core] perf/core: Fix event->parent life-time issue

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     162c9e3faf58eef653c74d0c774e6583d9225467
Gitweb:        https://git.kernel.org/tip/162c9e3faf58eef653c74d0c774e6583d9225467
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Tue, 15 Apr 2025 12:12:52 +02:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 17 Apr 2025 14:21:15 +02:00

perf/core: Fix event->parent life-time issue

Due to an oversight in merging:

  da916e96e2de ("perf: Make perf_pmu_unregister() useable")

on top of:

  56799bc03565 ("perf: Fix hang while freeing sigtrap event")

.. it is now possible to hit put_event(EVENT_TOMBSTONE), which makes
the computer sad.

This also means that for the event->parent == EVENT_TOMBSTONE, the
put_event() matching inherit_event() has gone missing.

Previously this was done in perf_event_release_kernel() after calling
perf_remove_from_context(), but with it delegated to put_event(), this
case is now entirely missed, leading to leaks.

Fixes: da916e96e2de ("perf: Make perf_pmu_unregister() useable")
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Tested-by: kernel test robot <oliver.sang@xxxxxxxxx>
Tested-by: James Clark <james.clark@xxxxxxxxxx>
Tested-by: Venkat Rao Bagalkote <venkat88@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202504131701.941039cd-lkp@xxxxxxxxx
Link: https://lkml.kernel.org/r/20250415131446.GN5600@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 kernel/events/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1a19df9..43d87de 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2343,6 +2343,7 @@ static void perf_child_detach(struct perf_event *event)
 	 * not being a child event. See for example unaccount_event().
 	 */
 	event->parent = EVENT_TOMBSTONE;
+	put_event(parent_event);
 }
 
 static bool is_orphaned_event(struct perf_event *event)
@@ -5688,7 +5689,7 @@ static void put_event(struct perf_event *event)
 	_free_event(event);
 
 	/* Matches the refcount bump in inherit_event() */
-	if (parent)
+	if (parent && parent != EVENT_TOMBSTONE)
 		put_event(parent);
 }