perf: Fix PERF_EVENT_IOC_PERIOD deadlock

Dmitry reported a fairly silly recursive lock deadlock for
PERF_EVENT_IOC_PERIOD, fix this by explicitly doing the inactive part of
__perf_event_period() instead of calling that function.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: c7999c6f3fed ("perf: Fix PERF_EVENT_IOC_PERIOD migration race")
Link: http://lkml.kernel.org/r/20151130115615.GJ17308@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5854fcf7f05a10a20f377089a34893b09d959530..49a5118f3564a8176067f123887a4da54a59547f 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4225,7 +4225,14 @@ retry:
                goto retry;
        }
 
-       __perf_event_period(&pe);
+       if (event->attr.freq) {
+               event->attr.sample_freq = value;
+       } else {
+               event->attr.sample_period = value;
+               event->hw.sample_period = value;
+       }
+
+       local64_set(&event->hw.period_left, 0);
        raw_spin_unlock_irq(&ctx->lock);
 
        return 0;