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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