Revert "UBUNTU: SAUCE: CacheFiles: fix a read_waiter/read_copier race"

BugLink: https://bugs.launchpad.net/bugs/1774336

Revert 9bd2e21f in Xenial.
Upstream has taken a different solution, which we're about to apply.
Signed-off-by: Daniel Axtens <daniel.axtens@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

fs/cachefiles/rdwr.c

@@ -58,9 +58,9 @@ static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
 
 	spin_lock(&object->work_lock);
 	list_add_tail(&monitor->op_link, &monitor->op->to_do);
-	fscache_enqueue_retrieval(monitor->op);
 	spin_unlock(&object->work_lock);
 
+	fscache_enqueue_retrieval(monitor->op);
 	return 0;
 }