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@intel.com>
Tested-by: kernel test robot <oliver.sang@intel.com>
Tested-by: James Clark <james.clark@linaro.org>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Closes: https://lore.kernel.org/oe-lkp/202504131701.941039cd-lkp@intel.com
Link: https://lkml.kernel.org/r/20250415131446.GN5600@noisy.programming.kicks-ass.net

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1a19df9d54fdb1d8da71ca18b94e3ff1eda8c1b7..43d87de3d4f247b82bde568a15478cdced7cf4b0 100644 (file)
--- 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);
 }