->write_super lock_super pushdown

Push down lock_super into ->write_super instances and remove it from the
caller.

Following filesystem don't need ->s_lock in ->write_super and are skipped:

 * bfs, nilfs2 - no other uses of s_lock and have internal locks in
	->write_super
 * ext2 - uses BKL in ext2_write_super and has internal calls without s_lock
 * reiserfs - no other uses of s_lock as has reiserfs_write_lock (BKL) in
 	->write_super
 * xfs - no other uses of s_lock and uses internal lock (buffer lock on
	superblock buffer) to serialize ->write_super.  Also xfs_fs_write_super
	is superflous and will go away in the next merge window

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/jffs2/super.c

@@ -56,15 +56,18 @@ static void jffs2_i_init_once(void *foo)
 static void jffs2_write_super(struct super_block *sb)
 {
 	struct jffs2_sb_info *c = JFFS2_SB_INFO(sb);
+
+	lock_super(sb);
 	sb->s_dirt = 0;
 
-	if (sb->s_flags & MS_RDONLY)
-		return;
+	if (!(sb->s_flags & MS_RDONLY)) {
+		D1(printk(KERN_DEBUG "jffs2_write_super()\n"));
+		jffs2_garbage_collect_trigger(c);
+		jffs2_erase_pending_blocks(c, 0);
+		jffs2_flush_wbuf_gc(c, 0);
+	}
 
-	D1(printk(KERN_DEBUG "jffs2_write_super()\n"));
-	jffs2_garbage_collect_trigger(c);
-	jffs2_erase_pending_blocks(c, 0);
-	jffs2_flush_wbuf_gc(c, 0);
+	unlock_super(sb);
 }
 
 static int jffs2_sync_fs(struct super_block *sb, int wait)