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Fix race between perf_event_free_task() and perf_event_release_kernel()

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that can result in missed wakeups and hung tasks.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'perf-urgent-2024-06-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull perf event fix from Ingo Molnar:
 "Fix race between perf_event_free_task() and perf_event_release_kernel()
  that can result in missed wakeups and hung tasks"

* tag 'perf-urgent-2024-06-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/core: Fix missing wakeup when waiting for context reference
This commit is contained in:
Linus Torvalds 2024-06-08 09:26:59 -07:00
commit 7cec2e16cb
1 changed files with 13 additions and 0 deletions
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13
kernel/events/core.c
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@ -5384,6 +5384,7 @@ int perf_event_release_kernel(struct perf_event *event)
again:
mutex_lock(&event->child_mutex);
list_for_each_entry(child, &event->child_list, child_list) {
void *var = NULL;
/*
* Cannot change, child events are not migrated, see the
@ -5424,11 +5425,23 @@ int perf_event_release_kernel(struct perf_event *event)
* this can't be the last reference.
*/
put_event(event);
} else {
var = &ctx->refcount;
}
mutex_unlock(&event->child_mutex);
mutex_unlock(&ctx->mutex);
put_ctx(ctx);
if (var) {
/*
* If perf_event_free_task() has deleted all events from the
* ctx while the child_mutex got released above, make sure to
* notify about the preceding put_ctx().
*/
smp_mb(); /* pairs with wait_var_event() */
wake_up_var(var);
}
goto again;
}
mutex_unlock(&event->child_mutex);