netdev - Re: [PATCH 1/3] virtio: fix virtio

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Message-Id: <200806141739.34341.rusty@rustcorp.com.au>
Date:	Sat, 14 Jun 2008 17:39:33 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mark McLoughlin <markmc@...hat.com>
Cc:	Jeff Garzik <jeff@...zik.org>, netdev@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 1/3] virtio: fix virtio_net xmit of freed skb bug

On Saturday 14 June 2008 00:14:00 Mark McLoughlin wrote:
> On Thu, 2008-05-29 at 16:34 +1000, Rusty Russell wrote:
> > On Tuesday 27 May 2008 21:06:26 Mark McLoughlin wrote:
> > > On Mon, 2008-05-26 at 17:42 +1000, Rusty Russell wrote:
> > > > If we fail to transmit a packet, we assume the queue is full and put
> > > > the skb into last_xmit_skb.  However, if more space frees up before
> > > > we xmit it, we loop, and the result can be transmitting the same skb
> > > > twice.
> > > >
> > > > Fix is simple: set skb to NULL if we've used it in some way, and
> > > > check before sending.
> >
> > Great! It's a corner case, but it's no more complicated to do it your
> > way.
> >
> > Minor mod, I find it clearer to have the vi->last_xmit_skb = NULL; under
> > the branch:
> >
> > Subject: [PATCH] virtio_net: Delay dropping tx skbs
> > Date: Tue, 27 May 2008 12:06:26 +0100
> > From: Mark McLoughlin <markmc@...hat.com>
> >
> > Currently we drop the skb in start_xmit() if we have a
> > queued buffer and fail to transmit it.
> >
> > However, if we delay dropping it until we've stopped the
> > queue and enabled the tx notification callback, then there
> > is a chance space might become available for it.
>
> Hmm, we lost this one somewhere along the way ...

Good catch.  Looks like it got folded, but pre-folded version got merged.  
Sorry, I've restored it to my series.

Thanks,
Rusty.
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