| Date | Sat, 13 Jun 2015 00:50:00 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 06/12] x86/mm: Enable and use the arch_pgd_init_late() method |
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On 06/11, Ingo Molnar wrote: > > +void arch_pgd_init_late(struct mm_struct *mm, pgd_t *pgd) > +{ > + /* > + * This is called after a new MM has been made visible > + * in fork() or exec(). > + * > + * This barrier makes sure the MM is visible to new RCU > + * walkers before we initialize it, so that we don't miss > + * updates: > + */ > + smp_wmb();
I can't understand the comment and the barrier...
Afaics, we need to ensure that:
> + if (pgd_val(*pgd_src)) > + WRITE_ONCE(*pgd_dst, *pgd_src);
either we notice the recent update of this PGD, or (say) the subsequent sync_global_pgds() can miss the child.
How the write barrier can help?
Oleg.
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