afs: add afs_wq and use it instead of the system workqueue

flush_scheduled_work() is going away.  afs needs to make sure all the
works it has queued have finished before being unloaded and there can
be arbitrary number of pending works.  Add afs_wq and use it as the
flush domain instead of the system workqueue.

Also, convert cancel_delayed_work() + flush_scheduled_work() to
cancel_delayed_work_sync() in afs_mntpt_kill_timer().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: linux-afs@lists.infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/afs/server.c b/fs/afs/server.c
index 9fdc7fe..d59b751 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -238,8 +238,8 @@
 	if (atomic_read(&server->usage) == 0) {
 		list_move_tail(&server->grave, &afs_server_graveyard);
 		server->time_of_death = get_seconds();
-		schedule_delayed_work(&afs_server_reaper,
-				      afs_server_timeout * HZ);
+		queue_delayed_work(afs_wq, &afs_server_reaper,
+				   afs_server_timeout * HZ);
 	}
 	spin_unlock(&afs_server_graveyard_lock);
 	_leave(" [dead]");
@@ -285,10 +285,11 @@
 		expiry = server->time_of_death + afs_server_timeout;
 		if (expiry > now) {
 			delay = (expiry - now) * HZ;
-			if (!schedule_delayed_work(&afs_server_reaper, delay)) {
+			if (!queue_delayed_work(afs_wq, &afs_server_reaper,
+						delay)) {
 				cancel_delayed_work(&afs_server_reaper);
-				schedule_delayed_work(&afs_server_reaper,
-						      delay);
+				queue_delayed_work(afs_wq, &afs_server_reaper,
+						   delay);
 			}
 			break;
 		}
@@ -323,5 +324,5 @@
 {
 	afs_server_timeout = 0;
 	cancel_delayed_work(&afs_server_reaper);
-	schedule_delayed_work(&afs_server_reaper, 0);
+	queue_delayed_work(afs_wq, &afs_server_reaper, 0);
 }