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Subject: Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg
To:     Tejun Heo <tj@kernel.org>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     hch@infradead.org, josef@toxicpanda.com, axboe@kernel.dk,
        cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
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From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <e27ea63a-8dd5-afad-b5d6-deabf879d191@huaweicloud.com>
Date:   Mon, 16 Jan 2023 11:25:07 +0800
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Hi,

在 2023/01/14 1:16, Tejun Heo 写道:
> As we discussed before, you'd have to order the actual freeing by shifting
> the ref puts into the free_work. If you move `blkg_put(blkg->parent)` and
> `list_del_init(&blkg->q_node)` to blkg_free_workfn() (this will require
> adjustments as these things are used from other places too), the free work
> items will be ordered and the blkg would remain iterable - IOW,
> deactivate_policy would be able to see it allowing the two paths to
> synchronize, right?

That sounds reasonable to only remove blkg from queue list if
pd_free_fn() is done.

It's right this way deactivate_policy will be able to see it, and if
deactivate_policy is called first, pd_free_fn() can be called here, and
later blkg_free_workfn() should skip pd_free_fn().

It's glad that we come up with suitable solution finially. ????

BTW, it might take some time before I send a new patchset cause Spring
Festival is coming.

Thanks,
Kuai
> 
> Thanks.
>