[tip:perf/core] perf/core: Plug potential memory leak in CPU_UP_PREPARE

[tip-bot for Thomas Gleixner]

Commit-ID:  059fcd8cd16622da6513804a7a3e826d152c6c96
Gitweb:     http://git.kernel.org/tip/059fcd8cd16622da6513804a7a3e826d152c6c96
Author:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Tue, 9 Feb 2016 20:11:34 +0000
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 17 Feb 2016 10:37:30 +0100

perf/core: Plug potential memory leak in CPU_UP_PREPARE

If CPU_UP_PREPARE is called it is not guaranteed, that a previously allocated
and assigned hash has been freed already, but perf_event_init_cpu()
unconditionally allocates and assignes a new hash if the swhash is referenced.
By overwriting the pointer the existing hash is not longer accessible.

Verify that there is no hash assigned on this cpu before allocating and
assigning a new one.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20160209201007.843269966@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4aa64a8..0d58522 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9206,7 +9206,7 @@ static void perf_event_init_cpu(int cpu)
 	struct swevent_htable *swhash = &per_cpu(swevent_htable, cpu);
 
 	mutex_lock(&swhash->hlist_mutex);
-	if (swhash->hlist_refcount > 0) {
+	if (swhash->hlist_refcount > 0 && !swevent_hlist_deref(swhash)) {
 		struct swevent_hlist *hlist;
 
 		hlist = kzalloc_node(sizeof(*hlist), GFP_KERNEL, cpu_to_node(cpu));