Re: [PATCH v4 06/19] irqdomain: Drop revmap mutex

Johan Hovold
2023-01-18T10:15:40Z

On Tue, Jan 17, 2023 at 10:23:20PM +0100, Thomas Gleixner wrote:
> On Mon, Jan 16 2023 at 14:50, Johan Hovold wrote:
> > The global irq_domain_mutex is now held in all paths that update the
> > revmap structures so there is no longer any need for the revmap mutex.
>
> This can also go after the 3rd race fix, but ...
>
> > static void irq_domain_clear_mapping(struct irq_domain *domain,
> > irq_hw_number_t hwirq)
> > {
> > + lockdep_assert_held(&irq_domain_mutex);
>
> these lockdep asserts want to be part of the [dis]association race
> fixes. They are completely unrelated to the removal of the revmap_mutex.

No, they are very much related to the removal of the revmap_mutex. These
functions deal with the revmap structures which before this patch were
clearly only modified with the revmap_mutex held.

The lockdep assert is here to guarantee that my claim that all current
(and future) paths that end up modifying these structures do so under
the irq_domain_mutex instead.

> Your race fixes change the locking and you want to ensure that all
> callers comply right there, no?

I want to make sure that all callers of these function comply, yes.
That's why the asserts belong in this patch.

Johan