netdev - Re: [PATCH] tcp: Fix for stalling connections

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Message-id: <4B1CE45A.9010908@tvk.rwth-aachen.de>
Date:	Mon, 07 Dec 2009 12:17:46 +0100
From:	Damian Lukowski <damian@....rwth-aachen.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	Frederic Leroy <fredo@...rox.org>,
	David Miller <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Greg KH <gregkh@...e.de>
Subject: Re: [PATCH] tcp: Fix for stalling connections

Eric Dumazet schrieb:
> Damian Lukowski a écrit :
>> This patch fixes a problem in the TCP connection timeout calculation.
>> Currently, timeout decisions are made on the basis of the current
>> tcp_time_stamp and retrans_stamp, which is usually set at the first
>> retransmission.
>> However, if the retransmission fails in tcp_retransmit_skb(),
>> retrans_stamp is not updated and remains zero. This leads to wrong
>> decisions in retransmits_timed_out() if tcp_time_stamp is larger than
>> the specified timeout, which is very likely.
>> In this case, the TCP connection dies after the first attempted
>> (and unsuccessful) retransmission.
>>
>> With this patch, tcp_skb_cb->when is used instead, when retrans_stamp
>> is not available.
>>
>> Thanks to Ilpo Järvinen for code suggestions.
>>
>> Signed-off-by: Damian Lukowski <damian@....rwth-aachen.de>
> 
> Hmm, how old is this bug ?
> 
> You should a hint of faulty commit so that stable team can apply
> this patch to 2.6.32 & 2.6.31
> 
> git describe 6fa12c85031485dff38ce550c24f10da23b0adaa
> 
> v2.6.31-rc5-1853-g6fa12c8

It has been introduced with retransmits_timed_out() in 2.6.32,
as timeout calculations have based on the number of
retransmissions before. The patch is needed for 2.6.32
and 2.6.33, but 2.6.31 does not use retransmits_timed_out().

> Or maybe David handles this for us, I dont know...
> 
> Minor note : retransmits_timed_out() is used in from net/ipv4/tcp_timer.c
> I wonder why its a "static inline" in include/net/tcp.h

I can place it in tcp_timer.c, if it's that, what you mean.

Regards.

> Thanks
> 
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