From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH RFC 4/7] virtio_blk: use dummy virtqueue_notify() to
	detect host kick error
Date: Wed, 23 Oct 2013 10:32:15 +1030
Message-ID: <8738nskg6w.fsf@rustcorp.com.au>
References: <1382445911-55657-1-git-send-email-graalfs@linux.vnet.ibm.com>
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To: Heinz Graalfs <graalfs@linux.vnet.ibm.com>, mst@redhat.com, virtualization@lists.linux-foundation.org
Cc: borntraeger@de.ibm.com
List-Id: virtualization@lists.linuxfoundation.org

Heinz Graalfs <graalfs@linux.vnet.ibm.com> writes:
> Deleting the disk and partitions in virtblk_remove() via del_gendisk() causes
> never ending waits when trying to synch dirty inode pages.
>
> A dummy virtqueue_notify() in virtblk_remove() is used to detect a host
> notification error, latter occurs when block device was hot-unplugged.
> When the dummy host kick failed blk_cleanup_queue() should be invoked
> prior to del_gendisk().
>
> Signed-off-by: Heinz Graalfs <graalfs@linux.vnet.ibm.com>
> ---
>  drivers/block/virtio_blk.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 6472395..98f081a 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -880,8 +880,14 @@ static void virtblk_remove(struct virtio_device *vdev)
>  	vblk->config_enable = false;
>  	mutex_unlock(&vblk->config_lock);
>  
> -	del_gendisk(vblk->disk);
> -	blk_cleanup_queue(vblk->disk->queue);
> +	virtqueue_notify(vblk->vq);
> +	if (virtqueue_is_broken(vblk->vq)) {
> +		blk_cleanup_queue(vblk->disk->queue);
> +		del_gendisk(vblk->disk);
> +	} else {
> +		del_gendisk(vblk->disk);
> +		blk_cleanup_queue(vblk->disk->queue);
> +	}

This seems horribly wrong.  Firstly, it's ugly to have a gratuitous
kick.  Secondly, it's racy: what if there's a hot unplug (or other
failure) after your virtqueue_is_broken() test?  We should be doing I/O
failures which should be handled by del_gendisk() correctly.

Cheers,
Rusty.