[ 3.5.y.z extended stable ] Patch "perf: Fix perf_cgroup_switch for sw-events" 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 perf_cgroup_switch for sw-events

to the linux-3.5.y-queue branch of the 3.5.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-3.5.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 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 0a3fce7570a1643feaea88e7546f3111ea64786c Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <a.p.zijlstra at chello.nl>
Date: Tue, 2 Oct 2012 15:41:23 +0200
Subject: [PATCH] perf: Fix perf_cgroup_switch for sw-events

commit 95cf59ea72331d0093010543b8951bb43f262cac upstream.

Jiri reported that he could trigger the WARN_ON_ONCE() in
perf_cgroup_switch() using sw-events. This is because sw-events share
a cpuctx with multiple PMUs.

Use the ->unique_pmu pointer to limit the pmu iteration to unique
cpuctx instances.

Reported-and-Tested-by: Jiri Olsa <jolsa at redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra at chello.nl>
Link: http://lkml.kernel.org/n/tip-so7wi2zf3jjzrwcutm2mkz0j@git.kernel.org
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Cc: Li Zefan <lizefan at huawei.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/events/core.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index b3a6de5..3ea14c1 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -368,6 +368,8 @@ void perf_cgroup_switch(struct task_struct *task, int mode)

 	list_for_each_entry_rcu(pmu, &pmus, entry) {
 		cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+		if (cpuctx->unique_pmu != pmu)
+			continue; /* ensure we process each cpuctx once */

 		/*
 		 * perf_cgroup_events says at least one
@@ -391,9 +393,10 @@ void perf_cgroup_switch(struct task_struct *task, int mode)

 			if (mode & PERF_CGROUP_SWIN) {
 				WARN_ON_ONCE(cpuctx->cgrp);
-				/* set cgrp before ctxsw in to
-				 * allow event_filter_match() to not
-				 * have to pass task around
+				/*
+				 * set cgrp before ctxsw in to allow
+				 * event_filter_match() to not have to pass
+				 * task around
 				 */
 				cpuctx->cgrp = perf_cgroup_from_task(task);
 				cpu_ctx_sched_in(cpuctx, EVENT_ALL, task);
--
1.8.3.2