netdev - Re: [BUG] tcp : how many times a frame can possibly be retransmitted ?

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Date:	Wed, 24 Aug 2011 21:45:32 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Zimmermann <alexander.zimmermann@...sys.rwth-aachen.de>
Cc:	netdev <netdev@...r.kernel.org>, Jerry Chu <hkchu@...gle.com>,
	Lukowski Damian <damian@....rwth-aachen.de>,
	Hannemann Arnd <arnd@...dnet.de>
Subject: Re: [BUG] tcp : how many times a frame can possibly be
 retransmitted ?

Le mercredi 24 août 2011 à 21:03 +0200, Alexander Zimmermann a écrit :
> Hi Eric,
> 
> Am 24.08.2011 um 18:21 schrieb Eric Dumazet:
> 
> > On one dev machine running net-next, I just found strange tcp sessions
> > that retransmit a frame forever (The other peer disappeared)
> 
> not forever...
> If remember correctly you will stop after 120s.
> 

Hi Alexander

I just tried again one session, and got much more delay than that.

It stops because of a side effect, "icsk_retransmits" being a 8bit
field.

Every 256 retransmits, it becomes 255+1 -> 0

retransmits_timed_out() immediately returns false.

And backoff increases at this time.

Eventually, we retransmit 256*15 times, process 256*15 ICMP messages.

Thanks


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