Re: [PATCH v2] blk-iocost: fix shift-out-of-bounds in iocg_hick_delay()

[Yu Kuai]

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;
+       }

> Thanks.