Re: [PATCH v3 RFC 3/4] virtio_blk: avoid calling blk_cleanup_queue() on device loss

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 27, 2013 at 11:32:39AM +0100, Heinz Graalfs wrote:
> Code is added to avoid calling blk_cleanup_queue() when the surprize_removal
> flag is set due to a disappeared device. It avoid hangs due to incomplete
> requests (e.g. in-flight requests). Such requests must be considered as lost.

Ugh. Can't we complete these immediately using detach_unused_buf? If not why?

> If the current remove callback was triggered due to an unregister driver,
> and the surprize_removal is not already set (although the actual device
> is already gone, e.g. virsh detach), blk_cleanup_queue() would be triggered
> resulting in a possible hang. This hang is caused by e.g. 'in-flight' requests
> that will never complete. This is a weird situation, and most likely not
> 'serializable'.

Hmm interesting. Implement some timeout and probe device to make sure
it's still alive?

> Signed-off-by: Heinz Graalfs <graalfs@linux.vnet.ibm.com>
> ---
>  drivers/block/virtio_blk.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 0f64282..8c05001 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -892,7 +892,8 @@ static void virtblk_remove(struct virtio_device *vdev)
>  	}
>  
>  	del_gendisk(vblk->disk);
> -	blk_cleanup_queue(vblk->disk->queue);
> +	if (!vdev->surprize_removal)
> +		blk_cleanup_queue(vblk->disk->queue);
>  
>  	/* Stop all the virtqueues. */
>  	vdev->config->reset(vdev);
> -- 
> 1.8.3.1