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

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

 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.

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

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