netdev - Re: [TCP]: Fix TCP header misalignment

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Date:	Sun, 18 Nov 2007 13:36:02 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	netdev@...r.kernel.org
Subject: Re: [TCP]: Fix TCP header misalignment

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Sun, 18 Nov 2007 20:15:30 +0800

> [TCP]: Fix TCP header misalignment
> 
> Indeed my previous change to alloc_pskb has made it possible
> for the TCP header to be misaligned iff the MTU is not a multiple
> of 4 (and less than a page).  So I suspect the optimised IPsec
> MTU calculation is giving you just such an MTU :)
> 
> This patch fixes it by changing alloc_pskb to make sure that
> the size is at least 32-bit aligned.  This does not cause the
> problem fixed by the previous patch because max_header is always
> 32-bit aligned which means that in the SG/NOTSO case this will
> be a no-op.
> 
> I thought about putting this in the callers but all the current
> callers are from TCP.  If and when we get a non-TCP caller we
> can always create a TCP wrapper for this function and move the
> alignment over there.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

I'm getting this without IPSEC FWIW.  I believe it occurs when I talk
to sites with sub-1500 MTUs.

I'll test your patch and let you know how it goes, thanks.
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