backport r13698 from 1.1: Do not use racy optimization when using blocking drivers

src/datawizard/data_request.c

@@ -173,6 +173,7 @@ int _starpu_wait_data_request_completion(struct _starpu_data_request *r, unsigne
 		}
 
 #ifndef STARPU_NON_BLOCKING_DRIVERS
+		/* XXX: shouldn't be needed, and doesn't work with chained requests anyway */
 		_starpu_wake_all_blocked_workers_on_node(r->handling_node);
 #endif
 
@@ -429,18 +430,24 @@ int _starpu_handle_node_data_requests(unsigned src_node, unsigned may_alloc, uns
 
 	*pushed = 0;
 
+#ifndef STARPU_NON_BLOCKING_DRIVERS
 	/* This is racy, but not posing problems actually, since we know we
 	 * will come back here to probe again regularly anyway.
 	 * Thus, do not expose this optimization to helgrind */
 	if (!RUNNING_ON_VALGRIND && _starpu_data_request_list_empty(data_requests[src_node]))
 		return 0;
+#endif
 
 	empty_list = _starpu_data_request_list_new();
 
+#ifdef STARPU_NON_BLOCKING_DRIVERS
 	/* take all the entries from the request list */
 	if (STARPU_PTHREAD_MUTEX_TRYLOCK(&data_requests_list_mutex[src_node]))
 		/* List is busy, do not bother with it */
 		return -EBUSY;
+#else
+	STARPU_PTHREAD_MUTEX_LOCK(&data_requests_list_mutex[src_node]);
+#endif
 
 	struct _starpu_data_request_list *local_list = data_requests[src_node];
 
@@ -518,18 +525,24 @@ void _starpu_handle_node_prefetch_requests(unsigned src_node, unsigned may_alloc
 
 	*pushed = 0;
 
+#ifndef STARPU_NON_BLOCKING_DRIVERS
 	/* This is racy, but not posing problems actually, since we know we
 	 * will come back here to probe again regularly anyway.
 	 * Thus, do not expose this optimization to valgrind */
 	if (!RUNNING_ON_VALGRIND && _starpu_data_request_list_empty(prefetch_requests[src_node]))
 		return;
+#endif
 
 	empty_list = _starpu_data_request_list_new();
 
+#ifdef STARPU_NON_BLOCKING_DRIVERS
 	/* take all the entries from the request list */
 	if (STARPU_PTHREAD_MUTEX_TRYLOCK(&data_requests_list_mutex[src_node]))
 		/* List is busy, do not bother with it */
 		return;
+#else
+	STARPU_PTHREAD_MUTEX_LOCK(&data_requests_list_mutex[src_node]);
+#endif
 
 	struct _starpu_data_request_list *local_list = prefetch_requests[src_node];