[BUG] lock issue in perf cgroup with jump label enabled

[Li Zefan]

With CONFIG_JUMP_LABEL enabled:

# mount -t cgroup -o perf_event xxx /mnt
# mkdir /mnt/test
# ./perf stat -B -a -e cycles:u -G test -- sleep 1

lockdep warning will be triggered immediately, and the machine
will become unresponsive.

I guess this is the culprit?

In the "perf cgroup support" patch:

@@ -419,6 +781,17 @@ list_add_event(struct perf_event *event, struct perf_event_con
                list_add_tail(&event->group_entry, list);
        }
 
+       if (is_cgroup_event(event)) {
+               ctx->nr_cgroups++;
+               /*
+                * one more event:
+                * - that has cgroup constraint on event->cpu
+                * - that may need work on context switch
+                */
+               atomic_inc(&per_cpu(perf_cgroup_events, event->cpu));
+               jump_label_inc(&perf_sched_events);
+       }

list_add_event() is called with spin lock ctl->lock held,  while
jump_label_inc() will acquire jump_label_mutex..
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