Messages in this thread Patch in this message | | | Date | Tue, 9 Sep 2014 07:53:54 -0700 | From | tip-bot for Cong Wang <> | Subject | [tip:perf/urgent] perf: Fix a race condition in perf_remove_from_context() |
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Commit-ID: 3577af70a2ce4853d58e57d832e687d739281479 Gitweb: http://git.kernel.org/tip/3577af70a2ce4853d58e57d832e687d739281479 Author: Cong Wang <cwang@twopensource.com> AuthorDate: Tue, 2 Sep 2014 15:27:20 -0700 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 9 Sep 2014 06:53:42 +0200
perf: Fix a race condition in perf_remove_from_context()
We saw a kernel soft lockup in perf_remove_from_context(), it looks like the `perf` process, when exiting, could not go out of the retry loop. Meanwhile, the target process was forking a child. So either the target process should execute the smp function call to deactive the event (if it was running) or it should do a context switch which deactives the event.
It seems we optimize out a context switch in perf_event_context_sched_out(), and what's more important, we still test an obsolete task pointer when retrying, so no one actually would deactive that event in this situation. Fix it directly by reloading the task pointer in perf_remove_from_context().
This should cure the above soft lockup.
Signed-off-by: Cong Wang <cwang@twopensource.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/1409696840-843-1-git-send-email-xiyou.wangcong@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/events/core.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c index f9c1ed0..d640a8b 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1524,6 +1524,11 @@ retry: */ if (ctx->is_active) { raw_spin_unlock_irq(&ctx->lock); + /* + * Reload the task pointer, it might have been changed by + * a concurrent perf_event_context_sched_out(). + */ + task = ctx->task; goto retry; } @@ -1967,6 +1972,11 @@ retry: */ if (ctx->is_active) { raw_spin_unlock_irq(&ctx->lock); + /* + * Reload the task pointer, it might have been changed by + * a concurrent perf_event_context_sched_out(). + */ + task = ctx->task; goto retry; }
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