linux-kernel - Re: [PATCH V2] virtio-blk: Ensure no requests in virtqueues before deleting vqs.

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Date: Tue, 30 Jan 2024 16:15:41 -0500
From: Stefan Hajnoczi <stefanha@...il.com>
To: Yi Sun <yi.sun@...soc.com>
Cc: stefanha@...hat.com, mst@...hat.com, jasowang@...hat.com, axboe@...nel.dk, 
	sunyibuaa@...il.com, hongyu.jin@...soc.com, zhiguo.niu@...soc.com, 
	xuanzhuo@...ux.alibaba.com, pbonzini@...hat.com, 
	virtualization@...ts.linux.dev, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] virtio-blk: Ensure no requests in virtqueues before
 deleting vqs.

On Mon, 29 Jan 2024 at 03:54, Yi Sun <yi.sun@...soc.com> wrote:
>
> Ensure no remaining requests in virtqueues before resetting vdev and
> deleting virtqueues. Otherwise these requests will never be completed.
> It may cause the system to become unresponsive.
>
> Function blk_mq_quiesce_queue() can ensure that requests have become
> in_flight status, but it cannot guarantee that requests have been
> processed by the device. Virtqueues should never be deleted before
> all requests become complete status.
>
> Function blk_mq_freeze_queue() ensure that all requests in virtqueues
> become complete status. And no requests can enter in virtqueues.
>
> Signed-off-by: Yi Sun <yi.sun@...soc.com>
> ---
>  drivers/block/virtio_blk.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>

>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 3b6b9abb8ce1..14ecc14ce8db 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1595,14 +1595,15 @@ static int virtblk_freeze(struct virtio_device *vdev)
>  {
>         struct virtio_blk *vblk = vdev->priv;
>
> +       /* Ensure no requests in virtqueues before deleting vqs. */
> +       blk_mq_freeze_queue(vblk->disk->queue);
> +
>         /* Ensure we don't receive any more interrupts */
>         virtio_reset_device(vdev);
>
>         /* Make sure no work handler is accessing the device. */
>         flush_work(&vblk->config_work);
>
> -       blk_mq_quiesce_queue(vblk->disk->queue);
> -
>         vdev->config->del_vqs(vdev);
>         kfree(vblk->vqs);
>
> @@ -1620,7 +1621,7 @@ static int virtblk_restore(struct virtio_device *vdev)
>
>         virtio_device_ready(vdev);
>
> -       blk_mq_unquiesce_queue(vblk->disk->queue);
> +       blk_mq_unfreeze_queue(vblk->disk->queue);
>         return 0;
>  }
>  #endif
> --
> 2.25.1
>
>