Messages in this thread | | | Date | Thu, 27 Jan 2022 13:22:47 +0100 | From | David Hildenbrand <> | Subject | Re: [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping |
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> > Yes, system_state can roughly separate these callers of __create_pgd_mapping. When system_state > SYSTEM_BOOTING we can add the lock. > Thus, I have the following change: > > static DEFINE_SPINLOCK(swapper_pgdir_lock); > +static DEFINE_MUTEX(fixmap_lock); > > void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd) > { > @@ -329,6 +330,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, > } > BUG_ON(p4d_bad(p4d)); > > + if (system_state > SYSTEM_BOOTING)
As there is nothing smaller than SYSTEM_BOOTING, you can use if (system_state != SYSTEM_BOOTING)
...
> > It seems work and somehow simper. But I don't know if it is reasonable to do this. So, any idea? @Ard Biesheuvel @Catalin Marinas
It's worth looking at kernel/notifier.c, e.g., blocking_notifier_chain_register()
if (unlikely(system_state == SYSTEM_BOOTING)) return notifier_chain_register(&nh->head, n);
down_write(&nh->rwsem); ret = notifier_chain_register(&nh->head, n); up_write(&nh->rwsem);
If we decide to go down that path, we should make sure to add a comment like
/* * No need for locking during early boot. And it doesn't work as * expected with KASLR enabled where we might clear BSS twice. */
-- Thanks,
David / dhildenb
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