netdev - Re: [PATCH] tcp: fix tcp_shift_skb_data() to not shift SACKed data below snd

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Message-Id: <20120306.151439.182216414366813515.davem@davemloft.net>
Date:	Tue, 06 Mar 2012 15:14:39 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ncardwell@...gle.com
Cc:	netdev@...r.kernel.org, ilpo.jarvinen@...sinki.fi,
	nanditad@...gle.com, ycheng@...gle.com, therbert@...gle.com
Subject: Re: [PATCH] tcp: fix tcp_shift_skb_data() to not shift SACKed data
 below snd_una

From: Neal Cardwell <ncardwell@...gle.com>
Date: Tue,  6 Mar 2012 00:35:04 -0500

> This commit fixes tcp_shift_skb_data() so that it does not shift
> SACKed data below snd_una.
> 
> This fixes an issue whose symptoms exactly match reports showing
> tp->sacked_out going negative since 3.3.0-rc4 (see "WARNING: at
> net/ipv4/tcp_input.c:3418" thread on netdev).
 ...
> After those two fixes, my testing has verified that shifting SACKed
> ranges below snd_una could cause tp->sacked_out to go negative with
> the following sequence of events:
> 
> (1) tcp_shift_skb_data() sees an skb whose end_seq is beyond snd_una,
>     then shifts a prefix of that skb that is below snd_una
 ...
> This fix changes tcp_shift_skb_data() to abort this sequence at step
> (1) in the scenario above by noticing that the bytes are below snd_una
> and not shifting them.
> 
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>

Applied and queued up for -stable, thanks.
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