Commit-ID: 3577af70a2ce4853d58e57d832e687d739281479 Gitweb: http://git.kernel.org/tip/3577af70a2ce4853d58e57d832e687d739281479 Author: Cong Wang <[email protected]> AuthorDate: Tue, 2 Sep 2014 15:27:20 -0700 Committer: Ingo Molnar <[email protected]> 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 <[email protected]> Signed-off-by: Cong Wang <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> Cc: Paul Mackerras <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- 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; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
