[PATCH] perf/core: make account/unaccount_sb_event consistent

[David Carrillo-Cisneros <davidcc@google.com>]

unaccount_pmu_sb_event did not check for attributes in event->attr
before calling detach_sb_event, while account_pmu_event did.

This caused NULL pointer reference in cgroup events that did not
have any of the attributes checked by account_pmu_event.

To trigger the bug just wait for a cgroup event to terminate, e.g.:

$ mkdir /dev/cgroup/devices/test
$ perf stat -e cycles -a -G test sleep 0

... see crash ...

Patch rebased on peterz/queue/perf/core .

Reviewed-by: Stephane Eranian <eranian@google.com>
Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 kernel/events/core.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1e48efc..6af0f01 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3682,15 +3682,28 @@ static void detach_sb_event(struct perf_event *event)
 	raw_spin_unlock(&pel->lock);
 }
 
-static void unaccount_pmu_sb_event(struct perf_event *event)
+static bool is_sb_event(struct perf_event *event)
 {
+	struct perf_event_attr *attr = &event->attr;
+
 	if (event->parent)
-		return;
+		return false;
 
 	if (event->attach_state & PERF_ATTACH_TASK)
-		return;
+		return false;
 
-	detach_sb_event(event);
+	if (attr->mmap || attr->mmap_data || attr->mmap2 ||
+	    attr->comm || attr->comm_exec ||
+	    attr->task ||
+	    attr->context_switch)
+		return true;
+	return false;
+}
+
+static void unaccount_pmu_sb_event(struct perf_event *event)
+{
+	if (is_sb_event(event))
+		detach_sb_event(event);
 }
 
 static void unaccount_event_cpu(struct perf_event *event, int cpu)
@@ -8666,18 +8679,7 @@ static void attach_sb_event(struct perf_event *event)
  */
 static void account_pmu_sb_event(struct perf_event *event)
 {
-	struct perf_event_attr *attr = &event->attr;
-
-	if (event->parent)
-		return;
-
-	if (event->attach_state & PERF_ATTACH_TASK)
-		return;
-
-	if (attr->mmap || attr->mmap_data || attr->mmap2 ||
-	    attr->comm || attr->comm_exec ||
-	    attr->task ||
-	    attr->context_switch)
+	if (is_sb_event(event))
 		attach_sb_event(event);
 }
 
-- 
2.8.0.rc3.226.g39d4020