[RFC][PATCH 3/7] perf: Allow perf_release() with !event->ctx

[Peter Zijlstra]

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.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
 kernel/events/core.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3754,9 +3754,19 @@ static void put_event(struct perf_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 @@ int perf_event_release_kernel(struct per
        }
        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);