Re: [PATCH 3/5] virtio_net: Add XDP support

On 16-11-18 03:21 PM, Eric Dumazet wrote:

On Fri, 2016-11-18 at 11:00 -0800, John Fastabend wrote:

quoted

 static void free_receive_bufs(struct virtnet_info *vi)
 {
+	struct bpf_prog *old_prog;
 	int i;
 
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		while (vi->rq[i].pages)
 			__free_pages(get_a_page(&vi->rq[i], GFP_KERNEL), 0);
+
+		old_prog = rcu_dereference(vi->rq[i].xdp_prog);

Seems wrong to me.

Yep it is wrong should be rtnl_dereference() here and the
rcu_dereference() calls earlier in the patch need to be _bh().

Are you sure lockdep (with CONFIG_PROVE_RCU=y) was happy with this ?

oops you are right it was missing.

quoted

+		RCU_INIT_POINTER(vi->rq[i].xdp_prog, NULL);
+		if (old_prog)
+			bpf_prog_put(old_prog);

bpf_prog_put() waits a grace period of ref count is zero. That said on
driver unload we need to protect the bpf_prog_put with RTNL_LOCK() as
well.

I'll send out a v2 in a bit.

Thanks a lot.

quoted

 	}
 }