ceph: Fix infinite loop in __wake_requests

__wake_requests() will enter infinite loop if we use it to wake
requests in the session->s_waiting list. __wake_requests() deletes
requests from the list and __do_request() adds requests back to
the list.
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Sage Weil <sage@inktank.com>

fs/ceph/mds_client.c

@@ -1876,9 +1876,14 @@ static int __do_request(struct ceph_mds_client *mdsc,
 static void __wake_requests(struct ceph_mds_client *mdsc,
 			    struct list_head *head)
 {
-	struct ceph_mds_request *req, *nreq;
+	struct ceph_mds_request *req;
+	LIST_HEAD(tmp_list);
+
+	list_splice_init(head, &tmp_list);
 
-	list_for_each_entry_safe(req, nreq, head, r_wait) {
+	while (!list_empty(&tmp_list)) {
+		req = list_entry(tmp_list.next,
+				 struct ceph_mds_request, r_wait);
 		list_del_init(&req->r_wait);
 		__do_request(mdsc, req);
 	}