Check if GCC uses assembler cfi support

[pf3gnuchains/gcc-fork.git] / libgomp / task.c

diff --git a/libgomp/task.c b/libgomp/task.c
index 4b75850..13e6605 100644 (file)
--- a/libgomp/task.c
+++ b/libgomp/task.c
@@ -116,11 +116,19 @@ GOMP_task (void (*fn) (void *), void *data, void (*cpyfn) (void *, void *),
        }
       else
        fn (data);
-      if (team != NULL)
+      /* Access to "children" is normally done inside a task_lock
+        mutex region, but the only way this particular task.children
+        can be set is if this thread's task work function (fn)
+        creates children.  So since the setter is *this* thread, we
+        need no barriers here when testing for non-NULL.  We can have
+        task.children set by the current thread then changed by a
+        child thread, but seeing a stale non-NULL value is not a
+        problem.  Once past the task_lock acquisition, this thread
+        will see the real value of task.children.  */
+      if (task.children != NULL)
        {
          gomp_mutex_lock (&team->task_lock);
-         if (task.children != NULL)
-           gomp_clear_parent (task.children);
+         gomp_clear_parent (task.children);
          gomp_mutex_unlock (&team->task_lock);
        }
       gomp_end_task ();
@@ -258,7 +266,13 @@ gomp_barrier_handle_tasks (gomp_barrier_state_t state)
                    parent->children = child_task->next_child;
                  else
                    {
-                     parent->children = NULL;
+                     /* We access task->children in GOMP_taskwait
+                        outside of the task lock mutex region, so
+                        need a release barrier here to ensure memory
+                        written by child_task->fn above is flushed
+                        before the NULL is written.  */
+                     __atomic_store_n (&parent->children, NULL,
+                                       MEMMODEL_RELEASE);
                      if (parent->in_taskwait)
                        gomp_sem_post (&parent->taskwait_sem);
                    }
@@ -291,7 +305,14 @@ GOMP_taskwait (void)
   struct gomp_task *child_task = NULL;
   struct gomp_task *to_free = NULL;
 
-  if (task == NULL || team == NULL)
+  /* The acquire barrier on load of task->children here synchronizes
+     with the write of a NULL in gomp_barrier_handle_tasks.  It is
+     not necessary that we synchronize with other non-NULL writes at
+     this point, but we must ensure that all writes to memory by a
+     child thread task work function are seen before we exit from
+     GOMP_taskwait.  */
+  if (task == NULL
+      || __atomic_load_n (&task->children, MEMMODEL_ACQUIRE) == NULL)
     return;
 
   gomp_mutex_lock (&team->task_lock);