Re: [PATCH] softirq: Provide a handshake for canceling tasklets via polling on PREEMPT_RT

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-08-13 08:05:34 [-1000], Tejun Heo wrote:
> Hello,
Hi Tejun,

> On Wed, Aug 13, 2025 at 08:33:11AM +0200, Sebastian Andrzej Siewior wrote:
> ...
> > > The intention is to convert all BH users to workqueue-BH and remove BH
> > > (that's what Linus wants and why workqueue-BH came to be), so the APIs
> > > should be able to match up, I'm afraid. There were some attempts at pushing
> > > the conversion but we've only made minimal progress. If you're looking at BH
> > > users anyway and feel like it, please feel free to convert them.
> > 
> > I understand this but I am talking about legacy users:
> > 
> > | drivers/atm/eni.c:      tasklet_disable_in_atomic(&ENI_DEV(vcc->dev)->task);
> > | drivers/net/wireless/ath/ath9k/beacon.c:        tasklet_disable_in_atomic(&sc->bcon_tasklet);
> > | drivers/pci/controller/pci-hyperv.c:    tasklet_disable_in_atomic(&channel->callback_event);
> > 
> > This is what is left. (There is also i915 but this is "special").
> > So we are talking about establishing an API and behaviour for those here
> > after we painfully managed converting everyone else away:
> 
> Right, given how early in conversion, we can definitely leave this as
> something to think about later. I have no objection to leave it be for now.

Okay. Do I need to update __flush_work() in anyway to make it obvious?
The local_bh_disable()/ local_bh_enable() will become a nop in this
regard and should be removed.
It would be the revert of commit 134874e2eee93 ("workqueue: Allow
cancel_work_sync() and disable_work() from atomic contexts on BH work
items"). The commit added the possibility to flush BH work from atomic
context but it is unclear if there already a requirement for this or if
it was to match the legacy part of the tasklet API.

> Thanks.

Sebastian