ceph: check migrate seq before changing auth cap

We may receive old request reply from the exporter MDS after receiving
the importer MDS' cap import message.
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>

fs/ceph/caps.c

@@ -612,9 +612,11 @@ int ceph_add_cap(struct inode *inode,
 		__cap_delay_requeue(mdsc, ci);
 	}
 
-	if (flags & CEPH_CAP_FLAG_AUTH)
+	if (flags & CEPH_CAP_FLAG_AUTH) {
+		if (ci->i_auth_cap == NULL ||
+		    ceph_seq_cmp(ci->i_auth_cap->mseq, mseq) < 0)
 			ci->i_auth_cap = cap;
-	else if (ci->i_auth_cap == cap) {
+	} else if (ci->i_auth_cap == cap) {
 		ci->i_auth_cap = NULL;
 		spin_lock(&mdsc->cap_dirty_lock);
 		if (!list_empty(&ci->i_dirty_item)) {