netdev - Re: [RFC PATCH] net: consolidate netif_needs

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Date:	Thu, 7 Jan 2010 16:07:21 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	john.r.fastabend@...el.com, netdev@...r.kernel.org
Subject: Re: [RFC PATCH] net: consolidate netif_needs_gso() checks

On Wed, Jan 06, 2010 at 08:34:23PM -0800, David Miller wrote:
> From: John Fastabend <john.r.fastabend@...el.com>
> Date: Mon, 04 Jan 2010 10:21:53 +0000
> 
> > netif_needs_gso() is checked twice in the TX path once,
> > before submitting the skb to the qdisc and once after
> > it is dequeued from the qdisc just before calling
> > ndo_hard_start().  This opens a window for a user to
> > change the gso/tso or tx checksum settings that can
> > cause netif_needs_gso to be true in one check and false
> > in the other.
> > 
> > Specifically, changing TX checksum setting may cause
> > the warning in skb_gso_segment() to be triggered if
> > the checksum is calculated earlier.
> > 
> > This consolidates the netif_needs_gso() calls so that
> > the stack only checks if gso is needed after the skb
> > is dequeued from the qdisc.  Or if the device has no
> > queue then before dev_hard_start_xmit() in dev_queue_xmit().
> > 
> > Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> 
> Herbert, please review.

Looks fine to me.  I have just one suggestion.  The queueless
case also calls dev_hard_start_xmit so we should be able to
remove the existing !need_gso code from dev_queue_xmit completely.

Thanks,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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