linux-kernel - Re: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum

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Date:	Wed, 01 Sep 2010 18:23:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	jarkao2@...il.com, pvp-lsts@...uni-ruse.bg,
	herbert@...dor.apana.org.au, rjw@...k.pl,
	kernel-testers@...r.kernel.org, maciej.rutecki@...il.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum_dev

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 01 Sep 2010 12:50:51 +0200

> [PATCH] gro: fix different skb headrooms
> 
> packets entering GRO might have different headrooms, even for a given
> flow (because of implementation details in drivers, like copybreak).
> We cant force drivers to deliver packets with a fixed headroom.
> 
> 1) fix skb_segment()
> 
> skb_segment() makes the false assumption headrooms of fragments are same
> than the head. When CHECKSUM_PARTIAL is used, this can give csum_start
> errors, and crash later in skb_copy_and_csum_dev()
> 
> 2) allocate a minimal skb for head of frag_list
> 
> skb_gro_receive() uses netdev_alloc_skb(headroom + skb_gro_offset(p)) to
> allocate a fresh skb. This adds NET_SKB_PAD to a padding already
> provided by netdevice, depending on various things, like copybreak.
> 
> Use alloc_skb() to allocate an exact padding, to reduce cache line
> needs:
> NET_SKB_PAD + NET_IP_ALIGN
> 
> bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=16626
> 
> Many thanks to Plamen Petrov, testing many debugging patches !
> With help of Jarek Poplawski.
> 
> Reported-by: Plamen Petrov <pvp-lsts@...uni-ruse.bg>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> CC: Jarek Poplawski <jarkao2@...il.com>

Good spotting, applied, thanks!
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