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Subject: Re: [PATCH] md: Don't clear MD_CLOSING when the raid is about to stop
To:     Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>,
        linan666@huaweicloud.com
Cc:     song@kernel.org, zlliu@suse.com, neilb@suse.com, shli@fb.com,
        linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, houtao1@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20231211081714.1923567-1-linan666@huaweicloud.com>
 <20231211105620.00001753@linux.intel.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <f0ab24e5-eb0a-d564-19d4-b72ecedff34f@huaweicloud.com>
Date:   Tue, 12 Dec 2023 11:21:28 +0800
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Hi,

?? 2023/12/11 17:56, Mariusz Tkaczyk д??:
> On Mon, 11 Dec 2023 16:17:14 +0800
> linan666@huaweicloud.com wrote:
> 
>> From: Li Nan <linan122@huawei.com>
>>
>> The raid should not be opened anymore when it is about to be stopped.
>> However, other processes can open it again if the flag MD_CLOSING is
>> cleared before exiting. From now on, this flag will not be cleared when
>> the raid will be stopped.
>>
>> Fixes: 065e519e71b2 ("md: MD_CLOSING needs to be cleared after called
>> md_set_readonly or do_md_stop") Signed-off-by: Li Nan <linan122@huawei.com>
> 
> Hello Li Nan,
> I was there when I needed to fix this:
> https://git.kernel.org/pub/scm/linux/kernel/git/song/md.git/commit/?h=md-next&id=c8870379a21fbd9ad14ca36204ccfbe9d25def43
> 
> For sure, you have to consider applying same solution for array_store "clear".
> Minor nit below.
> 
> Thanks,
> Mariusz
> 
>> ---
>>   drivers/md/md.c | 8 +++-----
>>   1 file changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index 4e9fe5cbeedc..ebdfc9068a60 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -6238,7 +6238,6 @@ static void md_clean(struct mddev *mddev)
>>   	mddev->persistent = 0;
>>   	mddev->level = LEVEL_NONE;
>>   	mddev->clevel[0] = 0;
>> -	mddev->flags = 0;
> 
> I recommend (safety recommendation):
> 	mddev->flags = MD_CLOSING;

Taking a look I think both MD_CLOSING and MD_DELETED should not be
cleared, however, there is no guarantee that MD_CLOSING will be set
before md_clean, because mdadm can be removed without running. Hence I
think just set MD_CLOSING is werid.

I think the proper way is to keep MD_CLOSING and MD_DELETED if they are
set. However, there is no such api to clear other bits at once. Since
we're not expecting anyone else to write flags, following maybe
acceptable:

mddev->flags &= BIT_ULL_MASK(MD_CLOSING) | BIT_ULL_MASK(MD_DELETED);

Or after making sure other flags cannot race, this patch is ok.

Thanks,
Kuai

> 
> Unless you can prove that other flags cannot race.
> 
>>   	mddev->sb_flags = 0;
>>   	mddev->ro = MD_RDWR;
>>   	mddev->metadata_type[0] = 0;
> 
> .
>