netdev - Re: [PATCH] tun: Persistent devices can get stuck in xoff state

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Date:	Thu, 10 Jul 2008 17:53:34 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	David Miller <davem@...emloft.net>
CC:	borntraeger@...ibm.com, netdev@...r.kernel.org
Subject: Re: [PATCH] tun: Persistent devices can get stuck in xoff state

David Miller wrote:
> From: Max Krasnyansky <maxk@...lcomm.com>
> Date: Wed, 09 Jul 2008 14:19:28 -0700
> 
>> Christian Borntraeger wrote:
>>> Am Mittwoch, 9. Juli 2008 schrieb Max Krasnyansky:
>>>> The scenario goes like this. App stops reading from tun/tap.
>>>> TX queue gets full and driver does netif_stop_queue().
>>>> App closes fd and TX queue gets flushed as part of the cleanup.
>>>> Next time the app opens tun/tap and starts reading from it but
>>>> the xoff state is not cleared. We're stuck.
>>>> Normally xoff state is cleared when netdev is brought up. But
>>>> in the case of persistent devices this happens only during
>>>> initial setup.
>>> I was able to reproduce the problem. The patch seems to fix it.
>>>
>>> Tested-by: Christian Borntraeger <borntraeger@...ibm.com>
>> Oh it definitely fixes that problem. It's very easy to reproduce by just 
>> suspending (ctrl-z) an app that is ready from the tun, waiting a bit for 
>> the queue to fill up and then killing the app. I have a simple test app 
>> that simulates this. It's just that in real life that does not happen 
>> very often. ie Applications either constantly read from tun or they 
>> close it.
>>
>> Thanks a lot for testing and confirming.
> 
> I've applied this, thanks.
> 
> But I had to apply it by hand.  You made this against an older
> tree, because in the current code there is a get_net() call
> right before the new lines you added but in your patch context
> it isn't there.

Hmm, I though I used latest git tree. Oh, turns out it was 2.6.25.4. 
Sorry. Thanx for fixing it.

Max



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