linux-kernel - Re: [dm-devel] [PATCH -next v2 2/6] md: refactor action

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Date:   Tue, 13 Jun 2023 20:44:24 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Xiao Ni <xni@...hat.com>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     guoqing.jiang@...ux.dev, agk@...hat.com, snitzer@...nel.org,
        dm-devel@...hat.com, song@...nel.org, yi.zhang@...wei.com,
        yangerkun@...wei.com, linux-kernel@...r.kernel.org,
        linux-raid@...r.kernel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [dm-devel] [PATCH -next v2 2/6] md: refactor action_store() for
 'idle' and 'frozen'

Hi,

在 2023/06/13 20:25, Xiao Ni 写道:
> On Tue, Jun 13, 2023 at 8:00 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>>
>> Hi,
>>
>> 在 2023/06/13 16:02, Xiao Ni 写道:
>>>
>>> 在 2023/5/29 下午9:20, Yu Kuai 写道:
>>>> From: Yu Kuai <yukuai3@...wei.com>
>>>>
>>>> Prepare to handle 'idle' and 'frozen' differently to fix a deadlock,
>>>> there
>>>> are no functional changes except that MD_RECOVERY_RUNNING is checked
>>>> again after 'reconfig_mutex' is held.
>>>
>>>
>>> Can you explain more about why it needs to check MD_RECOVERY_RUNNING
>>> again here?
>>
>> As I explain in the following comment:
> 
> Hi
> 
> Who can clear the flag before the lock is held?

Basically every where that can clear the flag...

// This context 	// Other context
			mutex_lock
			...
test_bit -> pass
			clear_bit
			mutex_unlock
mutex_lock
test_bit -> check again

Thanks,
Kuai
> 
> Regards
> Xiao
>>>> +    /*
>>>> +     * Check again in case MD_RECOVERY_RUNNING is cleared before lock is
>>>> +     * held.
>>>> +     */
>>>> +    if (!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) {
>>>> +        mddev_unlock(mddev);
>>>> +        return;
>>>> +    }
>>
>> Thanks,
>> Kuai
>>
> 
> .
>