From ac5b705b22642208764aa784ccc47f093d0212b5 Mon Sep 17 00:00:00 2001 From: Prakash Kamliya Date: Tue, 4 Feb 2014 16:08:35 -0800 Subject: [PATCH] staging: android: sync: Signal pt before sync_timeline object gets destroyed There is a race condition Assume we have *one* sync_fence object, with *one* sync_pt which belongs to *one* sync_timeline, given this condition, sync_timeline->kref will have two counts, one for sync_timeline (implicit) and another for sync_pt. Assume following is the situation on CPU Theead-1 : (Thread which calls sync_timeline_destroy()) -> (some function calls) -> sync_timeline_destory() -> sync_timeline_signal() (CPU is inside this function after putting reference to sync_timeline) At this time Thread-2 comes and does following Thread-2 : (fclose on fence fd) > sync_fence_release() -> because of fclose() on fence object -> sync_fence_free() -> sync_pt_free() -> kref_put(&pt->parent->kref, sync_timeline_free); -> sync_timeline_free() (CPU is inside this because this time kref will be zero after _put) Thread-2 will free sync_timeline object before Thread-1 has finished its work inside sync_timeline_signal. With this change we signals all sync_pt before putting reference to sync_timeline object. Cc: Colin Cross Cc: Android Kernel Team Signed-off-by: Prakash Kamliya [jstultz: minor commit subject tweak] Signed-off-by: John Stultz Signed-off-by: Greg Kroah-Hartman --- drivers/staging/android/sync.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c index b7fcaab0acea..3d05f662110b 100644 --- a/drivers/staging/android/sync.c +++ b/drivers/staging/android/sync.c @@ -92,14 +92,14 @@ static void sync_timeline_free(struct kref *kref) void sync_timeline_destroy(struct sync_timeline *obj) { obj->destroyed = true; + smp_wmb(); /* - * If this is not the last reference, signal any children - * that their parent is going away. + * signal any children that their parent is going away. */ + sync_timeline_signal(obj); - if (!kref_put(&obj->kref, sync_timeline_free)) - sync_timeline_signal(obj); + kref_put(&obj->kref, sync_timeline_free); } EXPORT_SYMBOL(sync_timeline_destroy); -- 2.20.1