On Mon, Dec 12, 2022 at 03:14:34PM +0100, Thomas Gleixner wrote: > On Fri, Dec 09 2022 at 15:01, Johan Hovold wrote: > > The IRQ domain structures are currently protected by the global > > irq_domain_mutex. Switch to using more fine-grained per-domain locking, > > which may potentially speed up parallel probing somewhat. > > > > Note that the domain lock of the root domain (innermost domain) must be > > used for hierarchical domains. For non-hierarchical domain (as for root > > domains), the new root pointer is set to the domain itself so that > > domain->root->mutex can be used in shared code paths. > > > > Also note that hierarchical domains should be constructed using > > irq_domain_create_hierarchy() (or irq_domain_add_hierarchy()) to avoid > > poking at irqdomain internals. > > While I agree in principle, this change really makes me nervous. > > Any fail in setting up domain->root correctly, e.g. by not using > irq_domain_create_hierarchy(), cannot be detected and creates nasty to > debug race conditions. > > So we need some debug mechanism which allows to validate that > domain->root is set up correctly when domain->parent != NULL. Lockdep will catch that due to the lockdep_assert_held(&domain->root->mutex); I added to irq_domain_set_mapping() and which is is called for each (inner) domain in a hierarchy when allocating an IRQ. Johan
