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

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

On 9/12/2026 5:09 PM, Michael S. Tsirkin wrote:
> 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 ...
> 
Got it. I will merge the detailed description of the issue into the
commit message.
> 
> 
> 
>> 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
>
Sure. Will remove this in the new patch.
> 
>> ---
>> 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?
>
I only CC in the mail, but not in the commit message, will add this in
the new patch.
> 
>> - 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>
>