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

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Date:   Wed, 3 Jul 2019 10:14:53 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, kvm@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2 0/3] vsock/virtio: several fixes in the .probe() and
 .remove()

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.

Stefan

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