On Mon, Jan 17, 2022 at 02:40:11PM +0800, Jason Wang
wrote:>
> ? 2022/1/15 ??5:43, Michael S. Tsirkin ??:
> > A common pattern for device reset is currently:
> > vdev->config->reset(vdev);
> > .. cleanup ..
> >
> > reset prevents new interrupts from arriving and waits for interrupt
> > handlers to finish.
> >
> > However if - as is common - the handler queues a work request which is
> > flushed during the cleanup stage, we have code adding buffers / trying
> > to get buffers while device is reset. Not good.
> >
> > This was reproduced by running
> > modprobe virtio_console
> > modprobe -r virtio_console
> > in a loop, and this reasoning seems to apply to virtio mem though
> > I could not reproduce it there.
> >
> > Fix this up by calling virtio_break_device + flush before reset.
> >
> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> > ---
> > drivers/virtio/virtio_mem.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> > index 38becd8d578c..33b8a118a3ae 100644
> > --- a/drivers/virtio/virtio_mem.c
> > +++ b/drivers/virtio/virtio_mem.c
> > @@ -2888,6 +2888,8 @@ static void virtio_mem_remove(struct
virtio_device *vdev)
> > virtio_mem_deinit_hotplug(vm);
> > /* reset the device and cleanup the queues */
> > + virtio_break_device(vdev);
> > + flush_work(&vm->wq);
>
>
> We set vm->removing to true and call cancel_work_sync() in
> virtio_mem_deinit_hotplug(). Isn't is sufficient?
>
> Thanks
Hmm I think you are right. David, I will drop this for now.
Up to you to consider whether some central capability will be
helpful as a replacement for the virtio-mem specific "removing" flag.
>
> > virtio_reset_device(vdev);
> > vdev->config->del_vqs(vdev);