Btrfs: don't flush all delalloc inodes when we doesn't get s_umount lock

We needn't flush all delalloc inodes when we doesn't get s_umount lock,
or we would make the tasks wait for a long time.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 57bc9f3..e174770 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4893,7 +4893,7 @@
 	case BTRFS_IOC_SYNC: {
 		int ret;
 
-		ret = btrfs_start_delalloc_roots(root->fs_info, 0);
+		ret = btrfs_start_delalloc_roots(root->fs_info, 0, -1);
 		if (ret)
 			return ret;
 		ret = btrfs_sync_fs(file->f_dentry->d_sb, 1);