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

[Stefan Hajnoczi <stefanha@redhat.com>]

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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().
> 
> Fixes: 7678abee0867 ("virtio-blk: don't keep queue frozen during system suspend")
> 
> Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>
> ---
> 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.
> ---
> Changes in v2:
> - Cc stable@vger.kernel.org.
> - 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(-)

Modulo Michael's comments about the commit message:

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

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