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

Vlastimil Babka
2017-04-12T08:18:21Z

On 04/12/2017 10:10 AM, Hillf Danton wrote:
> 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.

Ugh, thanks for catching this. Looks like my testing config didn't have
lockup detectors enabled.

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