netdev - Re: [PATCH RFC 1/2] vsock/virtio: fix kernel panic after device hot-unplug

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Date:   Thu, 3 Jan 2019 10:03:14 +0000
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH RFC 1/2] vsock/virtio: fix kernel panic after device
 hot-unplug

On Wed, Jan 02, 2019 at 11:01:27AM +0100, Stefano Garzarella wrote:
> On Wed, Jan 2, 2019 at 10:39 AM Stefan Hajnoczi <stefanha@...hat.com> wrote:
> >
> > On Thu, Dec 20, 2018 at 01:15:34PM +0100, Stefano Garzarella wrote:
> > > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > > index 5d3cce9e8744..9dae54698737 100644
> > > --- a/net/vmw_vsock/virtio_transport.c
> > > +++ b/net/vmw_vsock/virtio_transport.c
> > > @@ -75,6 +75,9 @@ static u32 virtio_transport_get_local_cid(void)
> > >  {
> > >       struct virtio_vsock *vsock = virtio_vsock_get();
> > >
> > > +     if (!vsock)
> > > +             return VMADDR_CID_ANY;
> > > +
> > >       return vsock->guest_cid;
> > >  }
> >
> > This looks unrelated to the rest of the patch.  Why is it necessary?
> 
> It is needed because the "the_virtio_vsock" returned by
> virtio_vsock_get() is initialized during the probe and freed during
> the removal.
> So, if we move the vsock_core_exit() in the virtio_vsock_exit(), can
> happen that the virtio_transport_get_local_cid() is called when the
> "the_virtio_vsock" is NULL.
> 
> Do you think is better to split this patch?

I'm curious which code paths reach virtio_transport_get_local_cid()
after the virtio device has been removed.  ioctl
IOCTL_VM_SOCKETS_GET_LOCAL_CID does.  Anything else?

Stefan

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