Re: [RFC 5/6] mm, cpuset: always use seqlock when changing task's nodemask

Hillf Danton
2017-04-12T08:10:53Z

On April 11, 2017 10:06 PM Vlastimil Babka wrote:
>
> static void cpuset_change_task_nodemask(struct task_struct *tsk,
> nodemask_t *newmems)
> {
> - bool need_loop;
> -
> task_lock(tsk);
> - /*
> - * Determine if a loop is necessary if another thread is doing
> - * read_mems_allowed_begin(). If at least one node remains unchanged and
> - * tsk does not have a mempolicy, then an empty nodemask will not be
> - * possible when mems_allowed is larger than a word.
> - */
> - need_loop = task_has_mempolicy(tsk) ||
> - !nodes_intersects(*newmems, tsk->mems_allowed);
>
> - if (need_loop) {
> - local_irq_disable();
> - write_seqcount_begin(&tsk->mems_allowed_seq);
> - }
> + local_irq_disable();
> + write_seqcount_begin(&tsk->mems_allowed_seq);
>
> - nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
> mpol_rebind_task(tsk, newmems);
> tsk->mems_allowed = *newmems;
>
> - if (need_loop) {
> - write_seqcount_end(&tsk->mems_allowed_seq);
> - local_irq_enable();
> - }
> + write_seqcount_end(&tsk->mems_allowed_seq);
>
Doubt if we'd listen irq again.

> task_unlock(tsk);
> }
> --
> 2.12.2