diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index bf4e22df7c97..e1b4a59485df 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3041,8 +3041,11 @@ out_wake_log_root:
 	mutex_unlock(&log_root_tree->log_mutex);
 
 	/*
-	 * The barrier before waitqueue_active is implied by mutex_unlock
+	 * The barrier before waitqueue_active is needed so all the updates
+	 * above are seen by the woken threads. It might not be necessary, but
+	 * proving that seems to be hard.
 	 */
+	smp_mb();
 	if (waitqueue_active(&log_root_tree->log_commit_wait[index2]))
 		wake_up(&log_root_tree->log_commit_wait[index2]);
 out:
@@ -3053,8 +3056,11 @@ out:
 	mutex_unlock(&root->log_mutex);
 
 	/*
-	 * The barrier before waitqueue_active is implied by mutex_unlock
+	 * The barrier before waitqueue_active is needed so all the updates
+	 * above are seen by the woken threads. It might not be necessary, but
+	 * proving that seems to be hard.
 	 */
+	smp_mb();
 	if (waitqueue_active(&root->log_commit_wait[index1]))
 		wake_up(&root->log_commit_wait[index1]);
 	return ret;