Re: [PATCH v2] virtio_blk: use synchronous quiesce in virtblk_freeze_priv()

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

On Sat, Sep 12, 2026 at 04:52:44PM +0800, Cong Zhang wrote:
> Replace blk_mq_quiesce_queue_nowait() with blk_mq_quiesce_queue() in
> virtblk_freeze_priv().
> 
> Keep the existing freeze and unfreeze order. The synchronous call waits
> for dispatch code that was already running. The queue remains quiesced
> until virtblk_restore_priv() calls blk_mq_unquiesce_queue().



This repeatition of the code in english is not what we need
in the commit log.

Suggested format:

The following issue was observed by ...: currently .... because ... this is a
problem because ... and we can not ... because ... to fix ... so that
... tested by ...: before ... after ...




> Fixes: 7678abee0867 ("virtio-blk: don't keep queue frozen during system suspend")
> 
> Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>

no empty lines between tags please

> ---
> blk_mq_run_work_fn() can call blk_mq_sched_dispatch_requests() through
> blk_mq_run_dispatch_ops(). The dispatcher checks QUEUE_FLAG_QUIESCED
> while the flag is clear. It can then be preempted before it gets a
> request. At that time, it has no queue usage reference, so
> blk_mq_freeze_queue() does not wait for it.
> 
> virtblk_freeze_priv() then calls blk_mq_quiesce_queue_nowait() and
> blk_mq_unfreeze_queue(). A new request can enter the queue. The old
> dispatcher can run again, use its old flag check, get the new request,
> and call virtio_queue_rq(). At the same time, virtblk_freeze_priv() can
> reset the device, delete the virtqueues, and free vblk->vqs. The old
> dispatcher can then use a deleted virtqueue or a NULL vblk->vqs, and the
> kernel can crash.



this kind of thing belongs in the commit log.

> ---
> Changes in v2:
> - Cc stable@vger.kernel.org.


which is no longer there?

> - Link to v1: https://lore.kernel.org/20260911-virtblk_sync_quiesce-v1-1-a883f8f31258@oss.qualcomm.com
> ---
>  drivers/block/virtio_blk.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 32bf3ba07a9d..7a570591e040 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1595,7 +1595,7 @@ static int virtblk_freeze_priv(struct virtio_device *vdev)
>  
>  	/* Ensure no requests in virtqueues before deleting vqs. */
>  	memflags = blk_mq_freeze_queue(q);
> -	blk_mq_quiesce_queue_nowait(q);
> +	blk_mq_quiesce_queue(q);
>  	blk_mq_unfreeze_queue(q, memflags);
>  
>  	/* Ensure we don't receive any more interrupts */
> 
> ---
> base-commit: 50d05c7c76c96b90462f24debacca971d2e86713
> change-id: 20260910-virtblk_sync_quiesce-9b2c88d45416
> 
> Best regards,
> --  
> Cong Zhang <cong.zhang@oss.qualcomm.com>