netdev - Re: [PATCH net 2/2] macvtap: read vnet_hdr

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Message-ID: <1486164469.21871.123.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Fri, 03 Feb 2017 15:27:49 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net 2/2] macvtap: read vnet_hdr_size once

On Fri, 2017-02-03 at 18:20 -0500, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> When IFF_VNET_HDR is enabled, a virtio_net header must precede data.
> Data length is verified to be greater than or equal to expected header
> length tun->vnet_hdr_sz before copying.
> 
> Macvtap functions read the value once, but unless READ_ONCE is used,
> the compiler may ignore this and read multiple times. Enforce a single
> read and locally cached value to avoid updates between test and use.
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> ---

Acked-by: Eric Dumazet <edumazet@...gle.com>