nfsd: allow more than one laundry job to run at a time

We can potentially have several nfs4_laundromat jobs running if there
are multiple namespaces running nfsd on the box. Those are effectively
separated from one another though, so I don't see any reason to
serialize them.

Also, create_singlethread_workqueue automatically adds the
WQ_MEM_RECLAIM flag. Since we run this job on a timer, it's not really
involved in any reclaim paths. I see no need for a rescuer thread.
Signed-off-by: NJeff Layton <jeff.layton@primarydata.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -6598,7 +6598,7 @@ nfs4_state_start(void)
 	ret = set_callback_cred();
 	if (ret)
 		return -ENOMEM;
-	laundry_wq = create_singlethread_workqueue("nfsd4");
+	laundry_wq = alloc_workqueue("%s", WQ_UNBOUND, 0, "nfsd4");
 	if (laundry_wq == NULL) {
 		ret = -ENOMEM;
 		goto out_recovery;