Re: [PATCH 3.10 06/31] tcp: tcp_make_synack() should clear skb->tstamp

[David Miller]

From: Willy Tarreau <w@xxxxxx>
Date: Mon, 27 Apr 2015 06:02:22 +0200

> 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@xxxxxxxxxx>
>> 
>> [ 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@xxxxxxxxxx>
>> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> ---
> 
> 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.

Eric Dumazet mentioned this and said it's harmless.
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