gfs2: Don't sleep during glock hash walk

In flush_delete_work, instead of flushing each individual pending
delayed work item, cancel and re-queue them for immediate execution.
The waiting isn't needed here because we're already waiting for all
queued work items to complete in gfs2_flush_delete_work.  This makes the
code more efficient, but more importantly, it avoids sleeping during a
rhashtable walk, inside rcu_read_lock().
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glock.c

@@ -1899,7 +1899,10 @@ bool gfs2_delete_work_queued(const struct gfs2_glock *gl)
 
 static void flush_delete_work(struct gfs2_glock *gl)
 {
-	flush_delayed_work(&gl->gl_delete);
+	if (cancel_delayed_work(&gl->gl_delete)) {
+		queue_delayed_work(gfs2_delete_workqueue,
+				   &gl->gl_delete, 0);
+	}
 	gfs2_glock_queue_work(gl, 0);
 }