Re: [dm-devel] [PATCH -next v2 2/6] md: refactor action_store() for 'idle' and 'frozen'

From: Yu Kuai <yukuai1@huaweicloud.com>
To: Xiao Ni <xni@redhat.com>, Yu Kuai <yukuai1@huaweicloud.com>
Cc: guoqing.jiang@linux.dev, agk@redhat.com, snitzer@kernel.org,
	dm-devel@redhat.com, song@kernel.org, yi.zhang@huawei.com,
	yangerkun@huawei.com, linux-kernel@vger.kernel.org,
	linux-raid@vger.kernel.org, "yukuai (C)" <yukuai3@huawei.com>
Subject: Re: [dm-devel] [PATCH -next v2 2/6] md: refactor action_store() for 'idle' and 'frozen'
Date: Tue, 13 Jun 2023 20:44:24 +0800	[thread overview]
Message-ID: <68b215a4-b4bb-7c94-6ad4-84ea859af742@huaweicloud.com> (raw)
In-Reply-To: <CALTww2-ta1NUJxcT3Dq5KP7iunnVx24X7RKj1OKYTYwEPeDNrg@mail.gmail.com>

Hi,

在 2023/06/13 20:25, Xiao Ni 写道:
> On Tue, Jun 13, 2023 at 8:00 PM Yu Kuai <yukuai1@huaweicloud.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@huawei.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
>>
> 
> .
> 