Re: [PATCH block/for-next] iocost: fix infinite loop bug in adjust_inuse_and_calc_cost()

[Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>]

On 9/14/20 9:05 AM, Tejun Heo wrote:
> adjust_inuse_and_calc_cost() is responsible for reducing the amount of
> donated weights dynamically in period as the budget runs low. Because we
> don't want to do full donation calculation in period, we keep latching up
> inuse by INUSE_ADJ_STEP_PCT of the active weight of the cgroup until the
> resulting hweight_inuse is satisfactory.
> 
> Unfortunately, the adj_step calculation was reading the active weight before
> acquiring ioc->lock. Because the current thread could have lost race to
> activate the iocg to another thread before entering this function, it may
> read the active weight as zero before acquiring ioc->lock. When this
> happens, the adj_step is calculated as zero and the incremental adjustment
> loop becomes an infinite one.
> 
> Fix it by fetching the active weight after acquiring ioc->lock.

Applied, thanks.

-- 
Jens Axboe