ceph: adding protection for showing cap reservation info

Adding spinlock protection during getting cap reservation
ralated fields so that the numbers match below BUG_ON condition
in the code.

BUG_ON(mdsc->caps_total_count != mdsc->caps_use_count +
				 mdsc->caps_reserve_count +
				 mdsc->caps_avail_count);

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

fs/ceph/caps.c

@@ -341,6 +341,8 @@ void ceph_reservation_status(struct ceph_fs_client *fsc,
 {
 	struct ceph_mds_client *mdsc = fsc->mdsc;
 
+	spin_lock(&mdsc->caps_list_lock);
+
 	if (total)
 		*total = mdsc->caps_total_count;
 	if (avail)
@@ -351,6 +353,8 @@ void ceph_reservation_status(struct ceph_fs_client *fsc,
 		*reserved = mdsc->caps_reserve_count;
 	if (min)
 		*min = mdsc->caps_min_count;
+
+	spin_unlock(&mdsc->caps_list_lock);
 }
 
 /*