On 2022/11/29 10:59, Yu Kuai wrote:
> Hi,
>
> 在 2022/11/29 10:49, Li Jinlin 写道:
>>
>>
>> On 2022/11/29 9:14, Yu Kuai wrote:
>>> Hi,
>>>
>>> 在 2022/11/29 3:58, Tejun Heo 写道:
>>>> On Mon, Nov 28, 2022 at 11:04:13AM +0800, Li Jinlin wrote:
>>>>> /* calculate the current delay in effect - 1/2 every second */
>>>>> tdelta = now->now - iocg->delay_at;
>>>>> if (iocg->delay)
>>>>> - delay = iocg->delay >> div64_u64(tdelta, USEC_PER_SEC);
>>>>> + delay = iocg->delay >>
>>>>> + min_t(u64, div64_u64(tdelta, USEC_PER_SEC), 63);
>>>>
>>>> I replied earlier but the right thing to do here is setting delay to 0 if
>>>> the shift is >= 64.
>>>
>>> Perhaps following change will make more sense?
>>>
>>> @@ -1322,18 +1323,19 @@ static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now)
>>> {
>>> struct ioc *ioc = iocg->ioc;
>>> struct blkcg_gq *blkg = iocg_to_blkg(iocg);
>>> - u64 tdelta, delay, new_delay;
>>> + u64 delay = 0;
>>> + u64 new_delay;
>>> s64 vover, vover_pct;
>>> u32 hwa;
>>>
>>> lockdep_assert_held(&iocg->waitq.lock);
>>>
>>> /* calculate the current delay in effect - 1/2 every second */
>>> - tdelta = now->now - iocg->delay_at;
>>> - if (iocg->delay)
>>> + if (iocg->delay && now->now > iocg->delay_at) {
>>> + u64 tdelta = now->now - iocg->delay_at;
>>> +
>>> delay = iocg->delay >> div64_u64(tdelta, USEC_PER_SEC);
>>> - else
>>> - delay = 0;
>>> + }
>>>
>> I think "now->now > iocg->delay_at" is unnecessary, it is almost inevitable.
>
> From what I see, following can only happen if now->now < iocg->delay_at:
>
> "shift exponent 18446744073709"
>
You are right.
But I didn't see any ubsan reported at now->now - iocg->delay_at.
Need to confirm this.
Jinlin
Thanks.
> Or something else triggers it?
>
> Thanks,
> Kuai
>
