netdev - Re: [PATCH] net: fix tp->undo_retrans accounting in tcp_sacktag

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Message-ID: <b1064d37-5510-c38b-d046-f914337cfe0b@chinatelecom.cn>
Date:   Fri, 10 Sep 2021 10:20:18 +0800
From:   zhenggy <zhenggy@...natelecom.cn>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, kuba@...nel.org
Subject: Re: [PATCH] net: fix tp->undo_retrans accounting in tcp_sacktag_one()

Hi，Neal：

Thanks very much for your checking, I will send a v2 patch to make it.

在 2021/9/9 21:38, Neal Cardwell 写道:
> On Thu, Sep 9, 2021 at 6:34 AM zhenggy <zhenggy@...natelecom.cn> wrote:
>>
>> Commit a71d77e6be1e ("tcp: fix segment accounting when DSACK range covers
>> multiple segments") fix some DSACK accounting for multiple segments.
>> In tcp_sacktag_one(), we should also use the actual DSACK rang(pcount)
>> for tp->undo_retrans accounting.
>>
>> Signed-off-by: zhenggy <zhenggy@...natelecom.cn>
>> ---
>>  net/ipv4/tcp_input.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index 3f7bd7a..141e85e 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -1346,7 +1346,7 @@ static u8 tcp_sacktag_one(struct sock *sk,
>>         if (dup_sack && (sacked & TCPCB_RETRANS)) {
>>                 if (tp->undo_marker && tp->undo_retrans > 0 &&
>>                     after(end_seq, tp->undo_marker))
>> -                       tp->undo_retrans--;
>> +                       tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
>>                 if ((sacked & TCPCB_SACKED_ACKED) &&
>>                     before(start_seq, state->reord))
>>                                 state->reord = start_seq;
>> --
> 
> Thanks for the fix!
> 
> I think it would be useful to have a Fixes: footer to help maintainers
> know how far back to backport the fix.
> 
> I think an appropriate fixes footer might be the following:
> 
> Fixes: 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time")
> 
> Before that commit, the assumption underlying the tp->undo_retrans--
> seems correct, AFAICT.
> 
> thanks,
> neal
>