xfs: xfs_iflush_cluster has range issues

xfs_iflush_cluster() does a gang lookup on the radix tree, meaning
it can find inodes beyond the current cluster if there is sparse
cache population. gang lookups return results in ascending index
order, so stop trying to cluster inodes once the first inode outside
the cluster mask is detected.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_inode.c

@@ -3207,11 +3207,20 @@ xfs_iflush_cluster(
 		 */
 		spin_lock(&iq->i_flags_lock);
 		if (!iq->i_ino ||
-		    __xfs_iflags_test(iq, XFS_ISTALE) ||
-		    (XFS_INO_TO_AGINO(mp, iq->i_ino) & mask) != first_index) {
+		    __xfs_iflags_test(iq, XFS_ISTALE)) {
 			spin_unlock(&iq->i_flags_lock);
 			continue;
 		}
+
+		/*
+		 * Once we fall off the end of the cluster, no point checking
+		 * any more inodes in the list because they will also all be
+		 * outside the cluster.
+		 */
+		if ((XFS_INO_TO_AGINO(mp, iq->i_ino) & mask) != first_index) {
+			spin_unlock(&iq->i_flags_lock);
+			break;
+		}
 		spin_unlock(&iq->i_flags_lock);
 
 		/*