Btrfs: make flushoncommit mount option correctly wait on ordered_extents

The commit_transaction call to wait_ordered_extents when snap_pending
passes nocow_only=1 to process only NOCOW or PREALLOC extents.  This isn't
correct for the 'flushoncommit' mode, as it skips extents we just started
IO on in start_delalloc_inodes.

So, in the flushoncommit case, wait on all ordered extents.  Otherwise,
only pass the nocow_only flag to wait_ordered_extents if snap_pending.
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/transaction.c

@@ -942,9 +942,11 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 		mutex_unlock(&root->fs_info->trans_mutex);
 
-		if (flush_on_commit || snap_pending) {
-			if (flush_on_commit)
+		if (flush_on_commit) {
 			btrfs_start_delalloc_inodes(root);
+			ret = btrfs_wait_ordered_extents(root, 0);
+			BUG_ON(ret);
+		} else if (snap_pending) {
 			ret = btrfs_wait_ordered_extents(root, 1);
 			BUG_ON(ret);
 		}