starpu_data_release: Fix unlocking post sync tasks

We want to unlock post sync tasks when we are last
(handle->post_sync_tasks_cnt == 1), but we don't actually want to decrement
the count when we are just downgrading the acquisition, since we will
call release again later, possibly to release more tasks that appeared
in between.

src/core/dependencies/implicit_data_deps.c

@@ -616,18 +616,25 @@ void _starpu_add_post_sync_tasks(struct starpu_task *post_sync_task, starpu_data
         _STARPU_LOG_OUT();
 }
 
-void _starpu_unlock_post_sync_tasks(starpu_data_handle_t handle)
+void _starpu_unlock_post_sync_tasks(starpu_data_handle_t handle, enum starpu_data_access_mode mode)
 {
 	struct _starpu_task_wrapper_list *post_sync_tasks = NULL;
 	unsigned do_submit_tasks = 0;
+	unsigned last_cnt;
 
 	/* Here helgrind would shout that this is an unprotected access, but
 	 * count can only be zero if we don't have to care about
 	 * post_sync_tasks_cnt at all.  */
-	if (STARPU_RUNNING_ON_VALGRIND || handle->post_sync_tasks_cnt)
+	if (handle->post_sync_tasks_cnt)
 	{
 		STARPU_PTHREAD_MUTEX_LOCK(&handle->sequential_consistency_mutex);
-		if (--handle->post_sync_tasks_cnt == 0)
+		last_cnt = handle->post_sync_tasks_cnt;
+
+		if (mode == STARPU_NONE)
+			/* Last release from us */
+			handle->post_sync_tasks_cnt--;
+
+		if (last_cnt == 1)
 		{
 			/* unlock all tasks : we need not hold the lock while unlocking all these tasks */
 			do_submit_tasks = 1;

src/core/dependencies/implicit_data_deps.h

@@ -30,7 +30,7 @@ void _starpu_release_data_enforce_sequential_consistency(struct starpu_task *tas
 void _starpu_release_task_enforce_sequential_consistency(struct _starpu_job *j);
 
 void _starpu_add_post_sync_tasks(struct starpu_task *post_sync_task, starpu_data_handle_t handle);
-void _starpu_unlock_post_sync_tasks(starpu_data_handle_t handle);
+void _starpu_unlock_post_sync_tasks(starpu_data_handle_t handle, enum starpu_data_access_mode mode);
 
 /** Register a hook to be called when a write is submitted */
 void _starpu_implicit_data_deps_write_hook(void (*func)(starpu_data_handle_t));

src/datawizard/user_interactions.c

@@ -500,7 +500,7 @@ void starpu_data_release_to_on_node(starpu_data_handle_t handle, enum starpu_dat
 		"We only support releasing from W to R");
 
 	/* In case there are some implicit dependencies, unlock the "post sync" tasks */
-	_starpu_unlock_post_sync_tasks(handle);
+	_starpu_unlock_post_sync_tasks(handle, mode);
 
 	/* The application can now release the rw-lock */
 	if (node >= 0)