[PATCH] quota: possible bug in quota format v2 support

Don't put root block of quota tree to the free list (when quota file is
completely empty).  That should not actually happen anyway (somebody should
get accounted for the filesystem root and so quota file should never be
empty) but better prevent it here than solve magical quota file
corruption.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/quota_v2.c

@@ -503,7 +503,8 @@ static int remove_tree(struct dquot *dquot, uint *blk, int depth)
 		int i;
 		ref[GETIDINDEX(dquot->dq_id, depth)] = cpu_to_le32(0);
 		for (i = 0; i < V2_DQBLKSIZE && !buf[i]; i++);	/* Block got empty? */
-		if (i == V2_DQBLKSIZE) {
+		/* Don't put the root block into the free block list */
+		if (i == V2_DQBLKSIZE && *blk != V2_DQTREEOFF) {
 			put_free_dqblk(sb, type, buf, *blk);
 			*blk = 0;
 		}