Re: [PATCH v3] virtio_blk: use synchronous quiesce in virtblk_freeze_priv()

[sashiko-bot@kernel.org]

> 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.
> 
> Fix this by using blk_mq_quiesce_queue(), which waits for dispatch code
> that was already running. Keep the existing freeze and unfreeze order.
> 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")
> Cc: stable@vger.kernel.org
> Acked-by: Jason Wang <jasowangio@gmail.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260928-virtblk_sync_quiesce-v3-1-a037e6e2fdf5@oss.qualcomm.com?part=1