netdev - Re: [PATCH] virtio-net: fix data corruption with OOM

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Message-ID: <20091026193417.GA26552@redhat.com>
Date:	Mon, 26 Oct 2009 21:34:17 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] virtio-net: fix data corruption with OOM

On Mon, Oct 26, 2009 at 08:42:43PM +0200, Michael S. Tsirkin wrote:
> On Mon, Oct 26, 2009 at 12:11:51PM +1030, Rusty Russell wrote:
> > On Mon, 26 Oct 2009 03:33:40 am Michael S. Tsirkin wrote:
> > > virtio net used to unlink skbs from send queues on error,
> > > but ever since 48925e372f04f5e35fec6269127c62b2c71ab794
> > > we do not do this. This causes guest data corruption and crashes
> > > with vhost since net core can requeue the skb or free it without
> > > it being taken off the list.
> > > 
> > > This patch fixes this by queueing the skb after successfull
> > > transmit.
> > 
> > I originally thought that this was racy: as soon as we do add_buf, we need to
> > make sure we're ready for the callback (for virtio_pci, it's ->kick, but we
> > shouldn't rely on that).
> 
> Modified the guest slightly, and I am getting crashes again.
> I didn't have time to debug this, but based on previous experience,
> I reverted 48925e372f04f5e35fec6269127c62b2c71ab794,
> and the crash went away.
> Rusty, what do you say we just revert 48925e372f04f5e35fec6269127c62b2c71ab794
> for now?

Hmm. Can't reproduce the crash anymore.
There is a small chance that the problem was my error,
so I guess I should try to reproduce and debug this,
after all.
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