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SubjectRe: [PATCH] virtio_console: break out of buf poll on remove
On Tue, Oct 05, 2021 at 03:04:07AM -0400, Michael S. Tsirkin wrote:
> 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.

That's a pathological case that is not "in the field" except by people
who want to abuse the system as root. And they can do much worse things
than that.

> Fixing this comprehensively needs some thought, and new APIs.
> Let's at least handle the specific case of virtio_console
> removal that was reported in the field.

Let's fix this correctly, don't just hack it up now.

> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1786239
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/char/virtio_console.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 7eaf303a7a86..c852ce0b4d56 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1956,6 +1956,12 @@ static void virtcons_remove(struct virtio_device *vdev)
> list_del(&portdev->list);
> spin_unlock_irq(&pdrvdata_lock);
>
> + /* Device is going away, exit any polling for buffers */
> + virtio_break_device(vdev);
> + if (use_multiport(portdev))
> + flush_work(&portdev->control_work);
> + else
> + flush_work(&portdev->config_work);
> /* Disable interrupts for vqs */

newline before comment?

thanks,

greg k-h

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