linux-kernel - Re: [PATCH] md: Don't clear MD_CLOSING when the raid is about to stop

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Date: Thu, 18 Jan 2024 09:49:48 +0800
From: Li Nan <linan666@...weicloud.com>
To: Yu Kuai <yukuai1@...weicloud.com>,
 Mariusz Tkaczyk <mariusz.tkaczyk@...ux.intel.com>, linan666@...weicloud.com
Cc: song@...nel.org, zlliu@...e.com, neilb@...e.com, shli@...com,
 linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, houtao1@...wei.com, yangerkun@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] md: Don't clear MD_CLOSING when the raid is about to stop



在 2023/12/12 11:21, Yu Kuai 写道:
> Hi,
> 
> 在 2023/12/11 17:56, Mariusz Tkaczyk 写道:
>> On Mon, 11 Dec 2023 16:17:14 +0800
>> linan666@...weicloud.com wrote:
>>
>>> From: Li Nan <linan122@...wei.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@...wei.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);
> 

MD_DELETED is only set after mddev->active is put to 0. We need to open 
mddev and get it before stropping raid, so the active must not be 0 and
MD_DELETED  will not be set in md_clean.

> 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;
>>
>> .
>>
> 
> 
> .

-- 
Thanks,
Nan