linux-kernel - Re: [PATCH -next 2/4] blk-iocost: don't throttle bio if iocg is offlined

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Message-ID: <Y6DXkLeOmu7VWovz@slm.duckdns.org>
Date:   Mon, 19 Dec 2022 11:28:48 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     hch@...radead.org, josef@...icpanda.com, axboe@...nel.dk,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yukuai3@...wei.com,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next 2/4] blk-iocost: don't throttle bio if iocg is
 offlined

On Sat, Dec 17, 2022 at 11:05:25AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> bio will grab blkg reference, however, blkcg->online_pin is not grabbed,
> hence cgroup can be removed after thread exit while bio is still in
> progress. Bypass io in this case since it doesn't make sense to
> throttle bio while cgroup is removed.

I don't get it. Why wouldn't that make sense? ISTR some occasions where we
clear the config to mitigate exits stalling for too long but in general a
policy being active on a draining cgroup shouldn't be a problem.

Thanks.

-- 
tejun