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

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Message-ID: <1479511316.8455.303.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Fri, 18 Nov 2016 15:21:56 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     tgraf@...g.ch, shm@...ulusnetworks.com,
        alexei.starovoitov@...il.com, daniel@...earbox.net,
        davem@...emloft.net, john.r.fastabend@...el.com,
        netdev@...r.kernel.org, bblanco@...mgrid.com, brouer@...hat.com
Subject: 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);
>  	}
>  }
>  
>