netdev - Re: [PATCH bpf-next v3 2/3] bpf: xdp, virtio_net use access ptr macro for xdp enable check

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Date:   Mon, 27 Jan 2020 11:02:53 +0100
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     bpf@...r.kernel.org, bjorn.topel@...el.com, songliubraving@...com,
        ast@...nel.org, daniel@...earbox.net, toke@...hat.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 2/3] bpf: xdp, virtio_net use access ptr
 macro for xdp enable check

On Sun, Jan 26, 2020 at 04:14:01PM -0800, John Fastabend wrote:
> virtio_net currently relies on rcu critical section to access the xdp
> program in its xdp_xmit handler. However, the pointer to the xdp program
> is only used to do a NULL pointer comparison to determine if xdp is
> enabled or not.
> 
> Use rcu_access_pointer() instead of rcu_dereference() to reflect this.
> Then later when we drop rcu_read critical section virtio_net will not
> need in special handling.
> 
> Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

Acked-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>