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

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Message-ID: <59987f54-47fc-766f-0667-5a90daca0b1a@kernel.dk>
Date:   Fri, 11 Sep 2020 16:43:18 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Tejun Heo <tj@...nel.org>
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 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.

-- 
Jens Axboe