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Date: Mon, 3 Feb 2014 10:16:18 -0800 From: John Stultz <john.stultz@...aro.org> To: LKML <linux-kernel@...r.kernel.org> Cc: Prakash Kamliya <pkamliya@...eaurora.org>, Colin Cross <ccross@...roid.com>, Android Kernel Team <kernel-team@...roid.com>, John Stultz <john.stultz@...aro.org> Subject: [PATCH 06/16] staging: sync: Signal pt before sync_timeline object gets destroyed From: Prakash Kamliya <pkamliya@...eaurora.org> 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. c: Greg KH <gregkh@...uxfoundation.org> Cc: Colin Cross <ccross@...roid.com> Cc: Android Kernel Team <kernel-team@...roid.com> Signed-off-by: Prakash Kamliya <pkamliya@...eaurora.org> [jstultz: minor commit subject tweak] Signed-off-by: John Stultz <john.stultz@...aro.org> --- 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 38e5d3b..fec2d1c 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); -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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