Re: [PATCH v2 0/3] vsock/virtio: several fixes in the .probe() and .remove()

From: Stefano Garzarella <sgarzare@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: netdev@vger.kernel.org, kvm@vger.kernel.org,
	"Michael S. Tsirkin" <mst@redhat.com>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Stefan Hajnoczi <stefanha@redhat.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH v2 0/3] vsock/virtio: several fixes in the .probe() and .remove()
Date: Wed, 3 Jul 2019 12:07:27 +0200	[thread overview]
Message-ID: <20190703100727.kuwpyc5sksrgmoxb@steredhat> (raw)
In-Reply-To: <20190703091453.GA11844@stefanha-x1.localdomain>

On Wed, Jul 03, 2019 at 10:14:53AM +0100, Stefan Hajnoczi wrote:
> On Mon, Jul 01, 2019 at 07:03:57PM +0200, Stefano Garzarella wrote:
> > On Mon, Jul 01, 2019 at 04:11:13PM +0100, Stefan Hajnoczi wrote:
> > > On Fri, Jun 28, 2019 at 02:36:56PM +0200, Stefano Garzarella wrote:
> > > > During the review of "[PATCH] vsock/virtio: Initialize core virtio vsock
> > > > before registering the driver", Stefan pointed out some possible issues
> > > > in the .probe() and .remove() callbacks of the virtio-vsock driver.
> > > > 
> > > > This series tries to solve these issues:
> > > > - Patch 1 adds RCU critical sections to avoid use-after-free of
> > > >   'the_virtio_vsock' pointer.
> > > > - Patch 2 stops workers before to call vdev->config->reset(vdev) to
> > > >   be sure that no one is accessing the device.
> > > > - Patch 3 moves the works flush at the end of the .remove() to avoid
> > > >   use-after-free of 'vsock' object.
> > > > 
> > > > v2:
> > > > - Patch 1: use RCU to protect 'the_virtio_vsock' pointer
> > > > - Patch 2: no changes
> > > > - Patch 3: flush works only at the end of .remove()
> > > > - Removed patch 4 because virtqueue_detach_unused_buf() returns all the buffers
> > > >   allocated.
> > > > 
> > > > v1: https://patchwork.kernel.org/cover/10964733/
> > > 
> > > This looks good to me.
> > 
> > Thanks for the review!
> > 
> > > 
> > > Did you run any stress tests?  For example an SMP guest constantly
> > > connecting and sending packets together with a script that
> > > hotplug/unplugs vhost-vsock-pci from the host side.
> > 
> > Yes, I started an SMP guest (-smp 4 -monitor tcp:127.0.0.1:1234,server,nowait)
> > and I run these scripts to stress the .probe()/.remove() path:
> > 
> > - guest
> >   while true; do
> >       cat /dev/urandom | nc-vsock -l 4321 > /dev/null &
> >       cat /dev/urandom | nc-vsock -l 5321 > /dev/null &
> >       cat /dev/urandom | nc-vsock -l 6321 > /dev/null &
> >       cat /dev/urandom | nc-vsock -l 7321 > /dev/null &
> >       wait
> >   done
> > 
> > - host
> >   while true; do
> >       cat /dev/urandom | nc-vsock 3 4321 > /dev/null &
> >       cat /dev/urandom | nc-vsock 3 5321 > /dev/null &
> >       cat /dev/urandom | nc-vsock 3 6321 > /dev/null &
> >       cat /dev/urandom | nc-vsock 3 7321 > /dev/null &
> >       sleep 2
> >       echo "device_del v1" | nc 127.0.0.1 1234
> >       sleep 1
> >       echo "device_add vhost-vsock-pci,id=v1,guest-cid=3" | nc 127.0.0.1 1234
> >       sleep 1
> >   done
> > 
> > Do you think is enough or is better to have a test more accurate?
> 
> That's good when left running overnight so that thousands of hotplug
> events are tested.

Honestly I run the test for ~30 mins (because without the patch the
crash happens in a few seconds), but of course, I'll run it this night :)

Thanks,
Stefano