> On 10/30/22 07:55, Jinlong Chen wrote:
> >>> So I think there is a redundant call to blk_freeze_queue_start(), we
> >>> just need to call blk_mq_freeze_queue_wait() after calling
> >>> blk_queue_start_drain().
> >>
> >> I think it is on purpose that blk_queue_start_drain() freezes the
> >> request queue and never unfreezes it. So if you want to change this
> >> behavior it's up to you to motivate why you want to change this behavior
> >> and also why it is safe to make that change. See also commit
> >> d3cfb2a0ac0b ("block: block new I/O just after queue is set as dying").
> >
> > I think there might be some misunderstanding. I didn't touch
> > blk_queue_start_drain(), so its behavior is not changed. What I have done
> > is just replacing blk_freeze_queue() with blk_mq_freeze_queue_wait() in
> > blk_mq_destroy_queue().
>
> Hi Jinlong,
>
> Does this mean that you want me to provide more information about what I
> wrote? Without this patch, blk_mq_destroy_queue() uses two mechanisms to
> block future I/O requests:
> 1. Set the flag QUEUE_FLAG_DYING.
> 2. Freeze the request queue and leave it frozen.
I agreed.
> Your patch modifies blk_mq_destroy_queue() such that it unfreezes the
> request queue after I/O has been quiesced instead of leaving it frozen.
This is what blk_mq_destroy_queue() looks like with the patch (removed
the stupid comment as suggested by Christoph Hellwig):
void blk_mq_destroy_queue(struct request_queue *q)
{
WARN_ON_ONCE(!queue_is_mq(q));
WARN_ON_ONCE(blk_queue_registered(q));
might_sleep();
blk_queue_flag_set(QUEUE_FLAG_DYING, q);
blk_queue_start_drain(q);
blk_mq_freeze_queue_wait(q);
blk_sync_queue(q);
blk_mq_cancel_work_sync(q);
blk_mq_exit_queue(q);
}
I can't see where the unfreezing happens. Did I miss something?
> I would appreciate it if Ming Lei (Cc-ed) could comment on this change
> since I think that Ming introduced (2) in blk_mq_destroy_queue()
> (formerly called blk_cleanup_queue()).
I would appreciate it too.
Thanks!
Jinlong Chen
