netdev - Re: [PATCH net] tcp: Don't collapse if resulting skb could overflow skb->csum

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Message-ID: <20130228164502.GD7558@casper.infradead.org>
Date:	Thu, 28 Feb 2013 16:45:02 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, foraker1@...l.gov
Subject: Re: [PATCH net] tcp: Don't collapse if resulting skb could overflow
 skb->csum_start

On 02/28/13 at 08:18am, Eric Dumazet wrote:
> but.... what is the value of skb_availroom(to) ?
> 
> The earlier test at line 2302 should already guard this case ?
> 
>                /* Punt if not enough space exists in the first SKB for
>                  * the data in the second
>                  */
>                 if (skb->len > skb_availroom(to))
>                         break;

Only if it is guaranteed that we never see an MSS > 64K.

Assuming that is true forever, then a21d45726 (tcp: avoid order-1
allocations on wifi and tx path) does in fact resolve this
issue at the cost of not being able to use the extra room
kmalloc() might have given us in __alloc_skb() for collapsing.

Was that an intentional side effect of a21d45726?
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