netdev - Re: scp stalls mysteriously

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Message-ID: <20091207231804.23baebd2@houba>
Date:	Mon, 7 Dec 2009 23:18:04 +0100
From:	Frederic Leroy <fredo@...rox.org>
To:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Cc:	Damian Lukowski <damian@....rwth-aachen.de>,
	Netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Greg KH <gregkh@...e.de>
Subject: Re: scp stalls mysteriously

Le Mon, 7 Dec 2009 16:01:53 +0200 (EET),
"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi> a écrit :

> On Sat, 5 Dec 2009, Damian Lukowski wrote:
> 
> > Could you please make another test and unplug the cable or drop
> > [...]
> After taking some more look into this, this is partly a red herring.
> It looks like that because of the place of the printk that was still
> in the end of the function. You can see the full trace of what
> happens in .13., they come from independent incarnations of RTO
> recovery (when finally no error happens in tcp_retransmit_skb).

Doh ! Sorry :( 

> However, the problem itself could occur. Here's the patch which
> should prevent that (I'm rather convinced that this really isn't
> stable worthy but net-next or net-2.6 would be fine):
> 
> --
> [PATCH] tcp: fix retrans_stamp advancing in error cases
> [...]

Tonight, I made 2 more tests : .20 and .21 . 

The first with latest damian patch from today.
Added the printk (This time I doubled checked ;).
Start the copy, wait 20s, disconnect cable 20s, reconnect. 

The second try was identical, but I added your patch.
The copy was slower comparing to the first try.

I didn't took time to understand tcp retransmission timeout and read
the code. So, I'm not sure the printk is at the good place and usefull.

-- 
Frédéric Leroy
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