netdev - Re: [PATCH bpf-next v2 2/3] bpf: xdp, virtio_net use access ptr macro for xdp enable check

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Message-ID: <20200126222850.04aff480@carbon>
Date:   Sun, 26 Jan 2020 22:28:50 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     brouer@...hat.com, bpf@...r.kernel.org, bjorn.topel@...el.com,
        songliubraving@...com, ast@...nel.org, daniel@...earbox.net,
        toke@...hat.com, maciej.fijalkowski@...el.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/3] bpf: xdp, virtio_net use access ptr
 macro for xdp enable check

On Sat, 25 Jan 2020 19:58:52 -0800
John Fastabend <john.fastabend@...il.com> 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.
> 
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer