linux-kernel - Re: [PATCH v2 block/for-next] blk-iocost: fix divide-by-zero in transfer

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Message-ID: <20200911224444.GB865564@mtj.thefacebook.com>
Date:   Fri, 11 Sep 2020 18:44:44 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, cgroups@...r.kernel.org
Subject: Re: [PATCH v2 block/for-next] blk-iocost: fix divide-by-zero in
 transfer_surpluses()

On Fri, Sep 11, 2020 at 04:43:18PM -0600, Jens Axboe wrote:
> On 9/11/20 4:40 PM, Tejun Heo wrote:
> > Conceptually, root_iocg->hweight_donating must be less than WEIGHT_ONE but
> > all hweight calculations round up and thus it may end up >= WEIGHT_ONE
> > triggering divide-by-zero and other issues. Bound the value to avoid
> > surprises.
> > 
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > Fixes: e08d02aa5fc9 ("blk-iocost: implement Andy's method for donation weight updates")
> > 
> > Signed-off-by: Tejun Heo <tj@...nel.org>
> > ---
> > Jens, I was flipping between doing max_t(, 1) over the whole divider and
> > doing min_t(, WEIGHT_ONE - 1) for hweight_donating. I thought that I as
> > testing after the last change but it obviously wasn't and the previous patch
> > doesn't compile due to missing type argument. Can you please apply this
> > patch instead? I can send an incremental patch if that'd be better. My
> > apologies.
> 
> Sure, I replaced it. BTW, you had two signed-off-by's in there.

Yeah, sloppy all around. Sorry about that. Gotta slow down more when posting
oh-shit-I-fucked-up stuff.

Thanks.

-- 
tejun