dma-buf: fix reservation_object_wait_timeout_rcu to wait correctly v2

With hardware resets in mind it is possible that all shared fences are
signaled, but the exlusive isn't. Fix waiting for everything in this situation.

v2: make sure we always wait for the exclusive fence
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1502384509-10465-3-git-send-email-alexander.deucher@amd.com

drivers/dma-buf/reservation.c

@@ -431,12 +431,25 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,
 	long ret = timeout ? timeout : 1;
 
 retry:
-	fence = NULL;
 	shared_count = 0;
 	seq = read_seqcount_begin(&obj->seq);
 	rcu_read_lock();
 
-	if (wait_all) {
+	fence = rcu_dereference(obj->fence_excl);
+	if (fence && !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
+		if (!dma_fence_get_rcu(fence))
+			goto unlock_retry;
+
+		if (dma_fence_is_signaled(fence)) {
+			dma_fence_put(fence);
+			fence = NULL;
+		}
+
+	} else {
+		fence = NULL;
+	}
+
+	if (!fence && wait_all) {
 		struct reservation_object_list *fobj =
 						rcu_dereference(obj->fence);
 
@@ -463,22 +476,6 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,
 		}
 	}
 
-	if (!shared_count) {
-		struct dma_fence *fence_excl = rcu_dereference(obj->fence_excl);
-
-		if (fence_excl &&
-		    !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
-			      &fence_excl->flags)) {
-			if (!dma_fence_get_rcu(fence_excl))
-				goto unlock_retry;
-
-			if (dma_fence_is_signaled(fence_excl))
-				dma_fence_put(fence_excl);
-			else
-				fence = fence_excl;
-		}
-	}
-
 	rcu_read_unlock();
 	if (fence) {
 		if (read_seqcount_retry(&obj->seq, seq)) {