Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v2 block/for-next] blk-iocost: fix divide-by-zero in
 transfer_surpluses()
To:     Tejun Heo <tj@kernel.org>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com, cgroups@vger.kernel.org
References: <20200911170746.GG4295@mtj.thefacebook.com>
 <ff46ca79-433e-3279-a8eb-35156639be7b@kernel.dk>
 <20200911224049.GA865564@mtj.thefacebook.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <59987f54-47fc-766f-0667-5a90daca0b1a@kernel.dk>
Date:   Fri, 11 Sep 2020 16:43:18 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20200911224049.GA865564@mtj.thefacebook.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@kernel.org>
> Fixes: e08d02aa5fc9 ("blk-iocost: implement Andy's method for donation weight updates")
> 
> Signed-off-by: Tejun Heo <tj@kernel.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