nilfs2: fix disorder of nilfs_write_super in nilfs_sync_fs

This fixes disorder of nilfs_write_super in nilfs_sync_fs.  Commiting
super block must be the end of the function so that every changes are
reflected.

->sync_fs() is not called frequently so this makes nilfs_sync_fs call
nilfs_commit_super instead of nilfs_write_super.
Signed-off-by: Jiro SEKIBA <jir@unicus.jp>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/super.c

@@ -385,13 +385,19 @@ static void nilfs_write_super(struct super_block *sb)
 
 static int nilfs_sync_fs(struct super_block *sb, int wait)
 {
+	struct nilfs_sb_info *sbi = NILFS_SB(sb);
+	struct the_nilfs *nilfs = sbi->s_nilfs;
 	int err = 0;
 
-	nilfs_write_super(sb);
-
 	/* This function is called when super block should be written back */
 	if (wait)
 		err = nilfs_construct_segment(sb);
+
+	down_write(&nilfs->ns_sem);
+	if (sb->s_dirt)
+		nilfs_commit_super(sbi, 1);
+	up_write(&nilfs->ns_sem);
+
 	return err;
 }