linux-kernel - Re: [PATCH v2] sched: Defend cfs and rt bandwidth quota against overflow

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Message-ID: <20200511130327.GA2978@hirez.programming.kicks-ass.net>
Date:   Mon, 11 May 2020 15:03:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     bsegall@...gle.com
Cc:     Huaixin Chang <changhuaixin@...ux.alibaba.com>,
        chiluk+linux@...eed.com, linux-kernel@...r.kernel.org,
        mingo@...hat.com, pauld@...head.com, vincent.guittot@...aro.org
Subject: Re: [PATCH v2] sched: Defend cfs and rt bandwidth quota against
 overflow

On Mon, Apr 27, 2020 at 11:29:30AM -0700, bsegall@...gle.com wrote:
> Huaixin Chang <changhuaixin@...ux.alibaba.com> writes:
> 
> > When users write some huge number into cpu.cfs_quota_us or
> > cpu.rt_runtime_us, overflow might happen during to_ratio() shifts of
> > schedulable checks.
> >
> > to_ratio() could be altered to avoid unnecessary internal overflow, but
> > min_cfs_quota_period is less than 1 << BW_SHIFT, so a cutoff would still
> > be needed. Set a cap MAX_BW for cfs_quota_us and rt_runtime_us to
> > prevent overflow.
> 
> Reviewed-by: Ben Segall <bsegall@...gle.com>

Thanks!