This is a note to let you know that I've just added the patch titled
perf: Fix a race condition in perf_remove_from_context()
to the 3.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-fix-a-race-condition-in-perf_remove_from_context.patch
and it can be found in the queue-3.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 3577af70a2ce4853d58e57d832e687d739281479 Mon Sep 17 00:00:00 2001
From: Cong Wang <[email protected]>
Date: Tue, 2 Sep 2014 15:27:20 -0700
Subject: perf: Fix a race condition in perf_remove_from_context()
From: Cong Wang <[email protected]>
commit 3577af70a2ce4853d58e57d832e687d739281479 upstream.
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]>
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
kernel/events/core.c | 10 ++++++++++
1 file changed, 10 insertions(+)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1523,6 +1523,11 @@ 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;
}
@@ -1966,6 +1971,11 @@ 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;
}
Patches currently in stable-queue which might be from [email protected] are
queue-3.16/perf-fix-a-race-condition-in-perf_remove_from_context.patch
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