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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.

Change-Id: Id1b5b20f99a6215a6f9532c4a87724302acbde3e
Original-Change-Id: Ia478a7650e0286968b9259eb4c87a72b3d95d368
Reported-and-Tested-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-so7wi2zf3jjzrwcutm2mkz0j@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Peter Zijlstra authored and chrmhoffmann committed Oct 2, 2012
1 parent 8b9ff4f commit fed4b99c5eb99ab792f223cefef67d940bbe8796
Showing with 6 additions and 3 deletions.
  1. +6 −3 kernel/events/core.c
@@ -371,6 +371,8 @@ 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
@@ -394,9 +396,10 @@ 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);

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