[3.11.y.z extended stable] Patch "perf: Fix hotplug splat" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    perf: Fix hotplug splat

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 4b7eed9bee386a4c14b356e779a69cf43d5fba73 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz at infradead.org>
Date: Mon, 24 Feb 2014 12:06:12 +0100
Subject: perf: Fix hotplug splat

commit e3703f8cdfcf39c25c4338c3ad8e68891cca3731 upstream.

Drew Richardson reported that he could make the kernel go *boom* when hotplugging
while having perf events active.

It turned out that when you have a group event, the code in
__perf_event_exit_context() fails to remove the group siblings from
the context.

We then proceed with destroying and freeing the event, and when you
re-plug the CPU and try and add another event to that CPU, things go
*boom* because you've still got dead entries there.

Reported-by: Drew Richardson <drew.richardson at arm.com>
Signed-off-by: Peter Zijlstra <peterz at infradead.org>
Cc: Will Deacon <will.deacon at arm.com>
Link: http://lkml.kernel.org/n/tip-k6v5wundvusvcseqj1si0oz0@git.kernel.org
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/events/core.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fc645f1..e074291 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7656,14 +7656,14 @@ static void perf_pmu_rotate_stop(struct pmu *pmu)
 static void __perf_event_exit_context(void *__info)
 {
 	struct perf_event_context *ctx = __info;
-	struct perf_event *event, *tmp;
+	struct perf_event *event;

 	perf_pmu_rotate_stop(ctx->pmu);

-	list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)
-		__perf_remove_from_context(event);
-	list_for_each_entry_safe(event, tmp, &ctx->flexible_groups, group_entry)
+	rcu_read_lock();
+	list_for_each_entry_rcu(event, &ctx->event_list, event_entry)
 		__perf_remove_from_context(event);
+	rcu_read_unlock();
 }

 static void perf_event_exit_cpu_context(int cpu)
@@ -7687,11 +7687,11 @@ static void perf_event_exit_cpu(int cpu)
 {
 	struct swevent_htable *swhash = &per_cpu(swevent_htable, cpu);

+	perf_event_exit_cpu_context(cpu);
+
 	mutex_lock(&swhash->hlist_mutex);
 	swevent_hlist_release(swhash);
 	mutex_unlock(&swhash->hlist_mutex);
-
-	perf_event_exit_cpu_context(cpu);
 }
 #else
 static inline void perf_event_exit_cpu(int cpu) { }
--
1.9.0