perf: Fix perf_cgroup_switch for sw-events

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@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>

1 files changed, 6 insertions, 3 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 81939e8999a5..fd15593c7f54 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -372,6 +372,8 @@ 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
@@ -395,9 +397,10 @@ 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);