rbd: barriers are hard (632b88ca) · Commits · 戴 / test

Let's go shopping! I'm afraid this may not have gotten it right: rbd: add barriers near done flag operations The smp_wmb() should have been done *before* setting the done flag, to ensure all other data was valid before marking the object request done. Switch to use atomic_inc_return() here to set the done flag, which allows us to verify we don't mark something done more than once. Doing this also implies general barriers before and after the call. And although a read memory barrier might have been sufficient before reading the done flag, convert this to a full memory barrier just to put this issue to bed. This resolves: http://tracker.ceph.com/issues/4238 Signed-off-by:

Alex Elder <elder@inktank.com> Reviewed-by:

Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

+12 −3

Original line number	Original line	Diff line number	Diff line
	@@ -1226,13 +1226,22 @@ static void obj_request_done_init(struct rbd_obj_request *obj_request)

	static void obj_request_done_set(struct rbd_obj_request *obj_request)		static void obj_request_done_set(struct rbd_obj_request *obj_request)
	{		{
	atomic_set(&obj_request->done, 1);		int done;
	smp_wmb();
			done = atomic_inc_return(&obj_request->done);
			if (done > 1) {
			struct rbd_img_request *img_request = obj_request->img_request;
			struct rbd_device *rbd_dev;

			rbd_dev = img_request ? img_request->rbd_dev : NULL;
			rbd_warn(rbd_dev, "obj_request %p was already done\n",
			obj_request);
			}
	}		}

	static bool obj_request_done_test(struct rbd_obj_request *obj_request)		static bool obj_request_done_test(struct rbd_obj_request *obj_request)
	{		{
	smp_rmb();		smp_mb();
	return atomic_read(&obj_request->done) != 0;		return atomic_read(&obj_request->done) != 0;
	}		}

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