netdev - Re: [PATCH v2] tcp: bug fix in proportional rate reduction.

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Message-Id: <20130523.001031.1071247701270523473.davem@davemloft.net>
Date:	Thu, 23 May 2013 00:10:31 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ycheng@...gle.com
Cc:	nanditad@...gle.com, netdev@...r.kernel.org, edumazet@...gle.com,
	ncardwell@...gle.com
Subject: Re: [PATCH v2] tcp: bug fix in proportional rate reduction.

From: Yuchung Cheng <ycheng@...gle.com>
Date: Tue, 21 May 2013 18:27:09 -0700

> On Tue, May 21, 2013 at 6:12 PM, Nandita Dukkipati <nanditad@...gle.com> wrote:
>> This patch is a fix for a bug triggering newly_acked_sacked < 0
>> in tcp_ack(.).
>>
>> The bug is triggered by sacked_out decreasing relative to prior_sacked,
>> but packets_out remaining the same as pior_packets. This is because the
>> snapshot of prior_packets is taken after tcp_sacktag_write_queue() while
>> prior_sacked is captured before tcp_sacktag_write_queue(). The problem
>> is: tcp_sacktag_write_queue (tcp_match_skb_to_sack() -> tcp_fragment)
>> adjusts the pcount for packets_out and sacked_out (MSS change or other
>> reason). As a result, this delta in pcount is reflected in
>> (prior_sacked - sacked_out) but not in (prior_packets - packets_out).
>>
>> This patch does the following:
>> 1) initializes prior_packets at the start of tcp_ack() so as to
>> capture the delta in packets_out created by tcp_fragment.
>> 2) introduces a new "previous_packets_out" variable that snapshots
>> packets_out right before tcp_clean_rtx_queue, so pkts_acked can be
>> correctly computed as before.
>> 3) Computes pkts_acked using previous_packets_out, and computes
>> newly_acked_sacked using prior_packets.
>>
>> Signed-off-by: Nandita Dukkipati <nanditad@...gle.com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>

Applied, and queued up for -stable, thanks.
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