linux-kernel - Re: [PATCH] virtio_mem: break device on remove

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Message-ID: <1f703ebf-0f78-e530-0fe1-163613397cad@redhat.com>
Date:   Mon, 17 Jan 2022 14:40:11 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio_mem: break device on remove


在 2022/1/15 上午5:43, Michael S. Tsirkin 写道:
> 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@...hat.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


>   	virtio_reset_device(vdev);
>   	vdev->config->del_vqs(vdev);
>