xfs: add a lock class for group/project dquots

We can have both a user and a group/project dquot locked at the same time,
as long as the user dquot is locked first.  Tell lockdep about that fact
by making the group/project dquots a different lock class.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>

fs/xfs/quota/xfs_dquot.c

@@ -73,6 +73,8 @@ int xfs_dqreq_num;
 int xfs_dqerror_mod = 33;
 #endif
 
+static struct lock_class_key xfs_dquot_other_class;
+
 /*
  * Allocate and initialize a dquot. We don't always allocate fresh memory;
  * we try to reclaim a free dquot if the number of incore dquots are above
@@ -141,6 +143,14 @@ xfs_qm_dqinit(
 #endif
 	}
 
+	/*
+	 * In either case we need to make sure group quotas have a different
+	 * lock class than user quotas, to make sure lockdep knows we can
+	 * locks of one of each at the same time.
+	 */
+	if (!(type & XFS_DQ_USER))
+		lockdep_set_class(&dqp->q_qlock, &xfs_dquot_other_class);
+
 	/*
 	 * log item gets initialized later
 	 */