perf: Allow perf_release() with !event->ctx

In the err_file: fput(event_file) case, the event will not yet have
been attached to a context. However perf_release() does assume it has
been. Cure this.

Tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174947.793996260@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 211a5ce..d5299e2 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3754,9 +3754,19 @@ static void put_event(struct perf_event *event)
  */
 int perf_event_release_kernel(struct perf_event *event)
 {
-       struct perf_event_context *ctx;
+       struct perf_event_context *ctx = event->ctx;
        struct perf_event *child, *tmp;
 
+       /*
+        * If we got here through err_file: fput(event_file); we will not have
+        * attached to a context yet.
+        */
+       if (!ctx) {
+               WARN_ON_ONCE(event->attach_state &
+                               (PERF_ATTACH_CONTEXT|PERF_ATTACH_GROUP));
+               goto no_ctx;
+       }
+
        if (!is_kernel_event(event))
                perf_remove_from_owner(event);
 
@@ -3832,8 +3842,8 @@ again:
        }
        mutex_unlock(&event->child_mutex);
 
-       /* Must be the last reference */
-       put_event(event);
+no_ctx:
+       put_event(event); /* Must be the 'last' reference */
        return 0;
 }
 EXPORT_SYMBOL_GPL(perf_event_release_kernel);