On Mon, Jan 10, 2022 at 05:49:09PM +0100, Christoph Hellwig wrote:
> On Tue, Jan 04, 2022 at 09:42:23PM +0800, Ming Lei wrote:
> > Commit cc9c884dd7f4 ("block: call submit_bio_checks under q_usage_counter")
> > uses q_usage_counter to protect submit_bio_checks for avoiding IO after
> > disk is deleted by del_gendisk().
> >
> > Turns out the protection isn't necessary, because once
> > blk_mq_freeze_queue_wait() in del_gendisk() returns:
> >
> > 1) all in-flight IO has been done
>
> Only for blk-mq drivers.
Yes, but the q_usage_counter protection for bio based queue is just for
calling ->submit_bio(), which is added in:
3ef28e83ab15 block: generic request_queue reference counting
Also we never support to drain in-flight IO for bio based queue, and
this patch doesn't make a difference on this area.
>
> So I don't think this is actually safe.
Draining bio based queue is always driver's responsibility, block
layer never supports that.
Thanks,
Ming
