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

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Message-ID: <Y77s0f741mFfGlTO@slm.duckdns.org>
Date:   Wed, 11 Jan 2023 07:07:29 -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 Wed, Jan 11, 2023 at 09:36:25AM +0800, Yu Kuai wrote:
> I'm not sure, of course this can fix the problem, but two spinlock
> 'blkcg->lock' and 'q->queue_lock' are used to protect blkg_destroy()
> currently, add a mutex（disk level?) requires a refactor, which seems
> complex to me.

The fact that the two paths can race each other already seems buggy. e.g.
What prevents them from running pd_free on the same pd twice? So, it needs
to be fixed anyway and the intention always has been that these callbacks
are called in the correct traversal order.

Thanks.

-- 
tejun