Re: [PATCH -next v2 9/9] blk-iocost: fix walk_list corruption

Yu Kuai
2022-12-01T13:43:34Z

在 2022/12/01 18:29, Tejun Heo 写道:
> On Thu, Dec 01, 2022 at 06:14:32PM +0800, Yu Kuai wrote:
>> Hi,
>>
>> 在 2022/12/01 18:00, Tejun Heo 写道:
>>> On Thu, Dec 01, 2022 at 09:19:54AM +0800, Yu Kuai wrote:
>>>>>> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
>>>>>> index 710cf63a1643..d2b873908f88 100644
>>>>>> --- a/block/blk-iocost.c
>>>>>> +++ b/block/blk-iocost.c
>>>>>> @@ -2813,13 +2813,14 @@ static void ioc_rqos_exit(struct rq_qos *rqos)
>>>>>> {
>>>>>> struct ioc *ioc = rqos_to_ioc(rqos);
>>>>>> + del_timer_sync(&ioc->timer);
>>>>>> +
>>>>>> blkcg_deactivate_policy(rqos->q, &blkcg_policy_iocost);
>>>>>> spin_lock_irq(&ioc->lock);
>>>>>> ioc->running = IOC_STOP;
>>>>>> spin_unlock_irq(&ioc->lock);
>>>>>> - del_timer_sync(&ioc->timer);
>>>>>
>>>>> I don't about this workaround. Let's fix properly?
>>>>
>>>> Ok, and by the way, is there any reason to delete timer after
>>>> deactivate policy? This seems a litter wreid to me.
>>>
>>> ioc->running is what controls whether the timer gets rescheduled or not. If
>>> we don't shut that down, the timer may as well get rescheduled after being
>>> deleted. Here, the only extra activation point is IO issue which shouldn't
>>> trigger during rq_qos_exit, so the ordering shouldn't matter but this is the
>>> right order for anything which can get restarted.
>>
>> Thanks for the explanation.
>>
>> I'm trying to figure out how to make sure child blkg pins it's parent,
>> btw, do you think following cleanup make sense?
>
> It's on you to explain why any change that you're suggesting is better and
> safe. I know it's not intentional but you're repeatedly suggesting operation
> reorderings in code paths which are really sensitive to ordering at least
> seemingly without putting much effort into thinking through the side
> effects. This costs disproportionate amount of review bandwidth, and
> increases the chance of new subtle bugs. Can you please slow down a bit and
> be more deliberate?

Thanks for the suggestion, I'll pay close attention to explain this "why
the change is better and safe". And sorry for the review pressure. 😔

>
> Thanks.
>