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Date: Sun, 26 Apr 2015 21:23:18 -0700
Message-ID: <CANn89iJA4Qxqs9KcuvNastSS-KMGyQi2tCLbHuXXzxeqjVArOA@mail.gmail.com>
Subject: Re: [PATCH 3.10 06/31] tcp: tcp_make_synack() should clear skb->tstamp
From: Eric Dumazet <edumazet@google.com>
To: Willy Tarreau <w@1wt.eu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>, stable@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>
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Right.

Bug was introduced in 3.18,  the Fixes: tag tells us ;)

git describe --contains 7faee5c0d514
v3.18-rc1~52^2~148^2

Note that it does not hurt having this backport to prior kernel versions.

Field is already 0 after skb allocation/cloning.



On Sun, Apr 26, 2015 at 9:02 PM, Willy Tarreau <w@1wt.eu> wrote:
> Hi Greg,
>
> On Sun, Apr 26, 2015 at 03:46:26PM +0200, Greg Kroah-Hartman wrote:
>> 3.10-stable review patch.  If anyone has any objections, please let me know.
>>
>> ------------------
>>
>> From: Eric Dumazet <edumazet@google.com>
>>
>> [ Upstream commit b50edd7812852d989f2ef09dcfc729690f54a42d ]
>>
>> I noticed tcpdump was giving funky timestamps for locally
>> generated SYNACK messages on loopback interface.
>>
>> 11:42:46.938990 IP 127.0.0.1.48245 > 127.0.0.2.23850: S
>> 945476042:945476042(0) win 43690 <mss 65495,nop,nop,sackOK,nop,wscale 7>
>>
>> 20:28:58.502209 IP 127.0.0.2.23850 > 127.0.0.1.48245: S
>> 3160535375:3160535375(0) ack 945476043 win 43690 <mss
>> 65495,nop,nop,sackOK,nop,wscale 7>
>>
>> This is because we need to clear skb->tstamp before
>> entering lower stack, otherwise net_timestamp_check()
>> does not set skb->tstamp.
>>
>> Fixes: 7faee5c0d514 ("tcp: remove TCP_SKB_CB(skb)->when")
>> Signed-off-by: Eric Dumazet <edumazet@google.com>
>> Signed-off-by: David S. Miller <davem@davemloft.net>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> ---
>
> Unless I missed something, the commit this patch fixes was not
> backported to 3.10 so I think we don't need this one. I have no
> idea whether it can have a side effect there though, Eric will
> probably know better.
>
> Thanks,
> Willy
>
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