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

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Date:	Thu, 10 Jul 2008 17:00:07 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	maxk@...lcomm.com
Cc:	borntraeger@...ibm.com, netdev@...r.kernel.org
Subject: Re: [PATCH] tun: Persistent devices can get stuck in xoff state

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.
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