perf: Fix 'perf sched record' deadlock

perf sched record can deadlock a box should the holder of
handle->data->lock take an interrupt, and then attempt to
acquire an rq lock held by a CPU trying to acquire the
same lock. Disable interrupts.

   CPU0                            CPU1
   sched event with rq->lock held
                                   grab handle->data->lock
   spin on handle->data->lock
                                   interrupt
                                   try to grab rq->lock

Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Tested-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1269598293.6174.8.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index b0feb47..96aae13 100644 (file)
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3376,15 +3376,23 @@ static void perf_event_task_output(struct perf_event *event,
                                     struct perf_task_event *task_event)
 {
        struct perf_output_handle handle;
-       int size;
        struct task_struct *task = task_event->task;
-       int ret;
+       unsigned long flags;
+       int size, ret;
+
+       /*
+        * If this CPU attempts to acquire an rq lock held by a CPU spinning
+        * in perf_output_lock() from interrupt context, it's game over.
+        */
+       local_irq_save(flags);
 
        size  = task_event->event_id.header.size;
        ret = perf_output_begin(&handle, event, size, 0, 0);
 
-       if (ret)
+       if (ret) {
+               local_irq_restore(flags);
                return;
+       }
 
        task_event->event_id.pid = perf_event_pid(event, task);
        task_event->event_id.ppid = perf_event_pid(event, current);
@@ -3395,6 +3403,7 @@ static void perf_event_task_output(struct perf_event *event,
        perf_output_put(&handle, task_event->event_id);
 
        perf_output_end(&handle);
+       local_irq_restore(flags);
 }
 
 static int perf_event_task_match(struct perf_event *event)