linux-kernel - Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg

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Message-ID: <Y72wF/b0/xNRmP7f@slm.duckdns.org>
Date:   Tue, 10 Jan 2023 08:36:07 -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, yi.zhang@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg

Hello,

On Tue, Jan 10, 2023 at 09:39:44AM +0800, Yu Kuai wrote:
> As I tried to explain before, we can make sure blkg_free() is called
> in order, but blkg_free() from remove cgroup can concurrent with
> deactivate policy, and we can't guarantee the order of ioc_pd_free()
> that is called both from blkg_free() and blkcg_deactivate_policy().
> Hence I don't think #3 is possible.

Hahaha, sorry that I keep forgetting that. This doesn't really feel like
that important or difficult part of the problem tho. Can't it be solved by
synchronizing blkg free work item against the deactivate path with a mutex?

Thanks.

-- 
tejun