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

[Cong Zhang <cong.zhang@oss.qualcomm.com>]

On 9/11/2026 10:22 AM, Jason Wang wrote:
> On Fri, Sep 11, 2026 at 12:31 AM Cong Zhang <cong.zhang@oss.qualcomm.com> 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")
>>
> 
> Do we need this for -stable?
> 
Good point, I will add this in V2.
>> 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.
>> ---
>>  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>
>>
> 
> Other than this,
> 
> Acked-by: Jason Wang <jasowangio@gmail.com>
> 
> Thanks