Re: [PATCH 7/8] dm-crypt: Convert from tasklet to BH workqueue

[Tejun Heo]

Hello,

On Tue, Jan 30, 2024 at 11:46:45AM +0100, Sebastian Andrzej Siewior wrote:
> On 2024-01-29 23:11:54 [-1000], Tejun Heo wrote:
> >  		if (in_hardirq() || irqs_disabled()) {
> > -			io->in_tasklet = true;
> > -			tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work);
> > -			tasklet_schedule(&io->tasklet);
> > +			INIT_WORK(&io->work, kcryptd_crypt);
> > +			queue_work(system_bh_wq, &io->work);
> 
> Why do we need the tasklet here in the first place? Couldn't we use
> workqueue? As per comment, the request originates in hardirq and then it
> is moved to tasklet. Couldn't it be moved to workqueue regardless?

Yes, you can and if you replace that system_bh_wq with system_wq, or
system_highpri_wq, everything should be fine in terms of correctness.
However, that would mean that the work item now would always incur a
scheduling latency which can be lengthy in certain circumstances. Whether
that's an actual problem for the subsystem at hand, I have no idea.

Thanks.

-- 
tejun