[PATCH 2/5] perf: Support disable() after stop() on software events

[Frederic Weisbecker <fweisbec@gmail.com>]

If we call perf_event_stop() on a software event and then the
disable() pmu callback on them after that, we'll call twice
hlist_del_rcu() on the same hlist node and then bring a crash
by dereferencing LIST_POISON2.

Just use hlist_del_init_rcu() instead to fix this problem.

This preparates for new context exclusions.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Zhang Yanmin <yanmin_zhang@linux.intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/perf_event.c             |    2 +-
 kernel/trace/trace_event_perf.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 95a56ed..c5f2306 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4292,7 +4292,7 @@ static int perf_swevent_enable(struct perf_event *event)
 
 static void perf_swevent_disable(struct perf_event *event)
 {
-	hlist_del_rcu(&event->hlist_entry);
+	hlist_del_init_rcu(&event->hlist_entry);
 }
 
 static void perf_swevent_void(struct perf_event *event)
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 4799d70..7bc1f26 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -122,7 +122,7 @@ int perf_trace_enable(struct perf_event *p_event)
 
 void perf_trace_disable(struct perf_event *p_event)
 {
-	hlist_del_rcu(&p_event->hlist_entry);
+	hlist_del_init_rcu(&p_event->hlist_entry);
 }
 
 void perf_trace_destroy(struct perf_event *p_event)
-- 
1.6.2.3