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

From: Peter Zijlstra
Date: Fri Feb 19 2016 - 09:50:29 EST


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) <peterz@xxxxxxxxxxxxx>
---
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);