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Subject: Re: Situation of CONFIG_BLK_WBT_MQ after commit b11d31ae01e6
 ("blk-wbt: remove unnecessary check in wbt_enable_default()")
To:     Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        Yu Kuai <yukuai1@huaweicloud.com>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "yukuai (C)" <yukuai3@huawei.com>
References: <CAKXUXMzfKq_J9nKHGyr5P5rvUETY4B-fxoQD4sO+NYjFOfVtZA@mail.gmail.com>
 <8a86ba08-cde4-97a4-d7e2-dc340609381c@huaweicloud.com>
 <CAKXUXMzA8GfJaWmdaszhrTtjMy5987oZ8AaBcoT6hNVvgCiZ-w@mail.gmail.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <40f7206a-350b-7522-79b0-35cd92e38017@huaweicloud.com>
Date:   Thu, 11 May 2023 16:38:05 +0800
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Hi,

在 2023/05/10 13:40, Lukas Bulwahn 写道:
> On Wed, May 10, 2023 at 5:24 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>
>> Hi,
>>
>> 在 2023/05/08 12:37, Lukas Bulwahn 写道:
>>> Dear Yu Kuai, dear Christoph, dear Jens,
>>>
>>>
>>> The commit b11d31ae01e6 ("blk-wbt: remove unnecessary check in
>>> wbt_enable_default()") removes the only reference to the config
>>> BLK_WBT_MQ in the kernel tree.
>>>
>>> The commit comes with the statement "If CONFIG_BLK_WBT_MQ is disabled,
>>> wbt_init() won't do anything.". The statement "If CONFIG_BLK_WBT is
>>> disabled, wbt_init() won't do anything." (note: CONFIG_BLK_WBT vs.
>>> CONFIG_BLK_WBT_MQ) is certainly true, but I do not see that "If
>>> CONFIG_BLK_WBT_MQ is disabled, wbt_init() won't do anything.", but I
>>> believe it would simply do what wbt_init() does with CONFIG_BLK_WBT
>>> being enabled.
>>>
>>> Now, it seems that with this commit applied, the intended switch of
>>> the config BLK_WBT_MQ is gone, and the config really now has no effect
>>> at all.
>>>
>>> So, I am a bit puzzled:
>>>
>>> 1. Either the config BLK_WBT_MQ does have an effect somewhere, but one
>>> cannot find its reference with 'git grep -i "BLK_WBT_MQ" .' --- so, my
>>> investigation is just incomplete or wrong, or
>>>
>>> 2. We really do not need this further build config BLK_WBT_MQ beyond
>>> the other configs already there --- then this config should just be
>>> removed, or
>>>
>>> 3. the commit unintentionally broke the purpose of the config
>>> BLK_WBT_MQ --- then this commit above should be reverted.
>>
>> Thanks for the report, it's the above case and it's my mistake.
>> I will fix this.
>>
> 
> Kuai, thanks for letting me know. Feel free to add a "Reported-by:
> Lukas Bulwahn <lukas.bulwahn@gmail.com>" tag, and to include in the
> list of recipients when you send out the fix to the mailing list.

I just send the fix, sorry that I forgot to cc you...

https://lore.kernel.org/all/20230511014509.679482-2-yukuai1@huaweicloud.com/

Thanks,
Kuai
> 
> I am glad to see that my investigation of kernel code is finding some
> issues that we can fix.
> 
> Lukas
> .
>