libceph: ceph-msgr workqueue needs a resque worker

commit f9865f06 upstream.

Commit f363e45f ("net/ceph: make ceph_msgr_wq non-reentrant")
effectively removed WQ_MEM_RECLAIM flag from ceph_msgr_wq.  This is
wrong - libceph is very much a memory reclaim path, so restore it.
Signed-off-by: Ilya Dryomov <idryomov@redhat.com>
Tested-by: Micha Krause <micha@krausam.de>
Reviewed-by: Sage Weil <sage@redhat.com>
[bwh: Backported to 3.2:
 - Keep passing the WQ_NON_REENTRANT flag too
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/ceph/messenger.c

@@ -99,7 +99,12 @@ struct workqueue_struct *ceph_msgr_wq;
 
 int ceph_msgr_init(void)
 {
-	ceph_msgr_wq = alloc_workqueue("ceph-msgr", WQ_NON_REENTRANT, 0);
+	/*
+	 * The number of active work items is limited by the number of
+	 * connections, so leave @max_active at default.
+	 */
+	ceph_msgr_wq = alloc_workqueue("ceph-msgr",
+				       WQ_NON_REENTRANT | WQ_MEM_RECLAIM, 0);
 	if (!ceph_msgr_wq) {
 		pr_err("msgr_init failed to create workqueue\n");
 		return -ENOMEM;