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/vlocation.c b/fs/afs/vlocation.c
index 9ac260d..431984d 100644
--- a/fs/afs/vlocation.c
+++ b/fs/afs/vlocation.c
@@ -507,8 +507,8 @@
 		_debug("buried");
 		list_move_tail(&vl->grave, &afs_vlocation_graveyard);
 		vl->time_of_death = get_seconds();
-		schedule_delayed_work(&afs_vlocation_reap,
-				      afs_vlocation_timeout * HZ);
+		queue_delayed_work(afs_wq, &afs_vlocation_reap,
+				   afs_vlocation_timeout * HZ);
 
 		/* suspend updates on this record */
 		if (!list_empty(&vl->update)) {
@@ -561,11 +561,11 @@
 		if (expiry > now) {
 			delay = (expiry - now) * HZ;
 			_debug("delay %lu", delay);
-			if (!schedule_delayed_work(&afs_vlocation_reap,
-						   delay)) {
+			if (!queue_delayed_work(afs_wq, &afs_vlocation_reap,
+						delay)) {
 				cancel_delayed_work(&afs_vlocation_reap);
-				schedule_delayed_work(&afs_vlocation_reap,
-						      delay);
+				queue_delayed_work(afs_wq, &afs_vlocation_reap,
+						   delay);
 			}
 			break;
 		}
@@ -620,7 +620,7 @@
 	destroy_workqueue(afs_vlocation_update_worker);
 
 	cancel_delayed_work(&afs_vlocation_reap);
-	schedule_delayed_work(&afs_vlocation_reap, 0);
+	queue_delayed_work(afs_wq, &afs_vlocation_reap, 0);
 }
 
 /*