ceph: avoid creating orphan object when checking pool permission

Pool permission check needs to write to the first object. But for
snapshot, head of the first object may have already been deleted.
Skip the check for snapshot inode to avoid creating orphan object.

Link: http://tracker.ceph.com/issues/18211
Signed-off-by: Yan, Zheng <zyan@redhat.com>

fs/ceph/addr.c

@@ -1948,6 +1948,15 @@ int ceph_pool_perm_check(struct ceph_inode_info *ci, int need)
 	struct ceph_string *pool_ns;
 	int ret, flags;
 
+	if (ci->i_vino.snap != CEPH_NOSNAP) {
+		/*
+		 * Pool permission check needs to write to the first object.
+		 * But for snapshot, head of the first object may have alread
+		 * been deleted. Skip check to avoid creating orphan object.
+		 */
+		return 0;
+	}
+
 	if (ceph_test_mount_opt(ceph_inode_to_client(&ci->vfs_inode),
 				NOPOOLPERM))
 		return 0;