ceph: optimize mds session register

Do memory allocation first, so that avoid unnecessary
initialization of newly allocated session in error case.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mds_client.c

@@ -448,6 +448,25 @@ static struct ceph_mds_session *register_session(struct ceph_mds_client *mdsc,
 	s = kzalloc(sizeof(*s), GFP_NOFS);
 	if (!s)
 		return ERR_PTR(-ENOMEM);
+
+	if (mds >= mdsc->max_sessions) {
+		int newmax = 1 << get_count_order(mds + 1);
+		struct ceph_mds_session **sa;
+
+		dout("%s: realloc to %d\n", __func__, newmax);
+		sa = kcalloc(newmax, sizeof(void *), GFP_NOFS);
+		if (!sa)
+			goto fail_realloc;
+		if (mdsc->sessions) {
+			memcpy(sa, mdsc->sessions,
+			       mdsc->max_sessions * sizeof(void *));
+			kfree(mdsc->sessions);
+		}
+		mdsc->sessions = sa;
+		mdsc->max_sessions = newmax;
+	}
+
+	dout("%s: mds%d\n", __func__, mds);
 	s->s_mdsc = mdsc;
 	s->s_mds = mds;
 	s->s_state = CEPH_MDS_SESSION_NEW;
@@ -476,23 +495,6 @@ static struct ceph_mds_session *register_session(struct ceph_mds_client *mdsc,
 	INIT_LIST_HEAD(&s->s_cap_releases);
 	INIT_LIST_HEAD(&s->s_cap_flushing);
 
-	dout("register_session mds%d\n", mds);
-	if (mds >= mdsc->max_sessions) {
-		int newmax = 1 << get_count_order(mds+1);
-		struct ceph_mds_session **sa;
-
-		dout("register_session realloc to %d\n", newmax);
-		sa = kcalloc(newmax, sizeof(void *), GFP_NOFS);
-		if (!sa)
-			goto fail_realloc;
-		if (mdsc->sessions) {
-			memcpy(sa, mdsc->sessions,
-			       mdsc->max_sessions * sizeof(void *));
-			kfree(mdsc->sessions);
-		}
-		mdsc->sessions = sa;
-		mdsc->max_sessions = newmax;
-	}
 	mdsc->sessions[mds] = s;
 	atomic_inc(&mdsc->num_sessions);
 	refcount_inc(&s->s_ref);  /* one ref to sessions[], one to caller */