linux-kernel - Re: [Patch v2] mm/migrate.c: also overwrite error when it is bigger than zero

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Message-ID: <0aa42c19-4144-5c7a-10f5-162b1b068d4c@nvidia.com>
Date:   Tue, 21 Jan 2020 11:33:16 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
CC:     <akpm@...ux-foundation.org>, <yang.shi@...ux.alibaba.com>,
        <vbabka@...e.cz>, <cl@...ux.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <mhocko@...nel.org>
Subject: Re: [Patch v2] mm/migrate.c: also overwrite error when it is bigger
 than zero

On 1/20/20 6:34 PM, Wei Yang wrote:
> On Tue, Jan 21, 2020 at 09:53:26AM +0800, Wei Yang wrote:
>> On Sun, Jan 19, 2020 at 02:57:53PM +0800, Wei Yang wrote:
>>> If we get here after successfully adding page to list, err would be
>>> 1 to indicate the page is queued in the list.
>>>
>>> Current code has two problems:
>>>
>>>   * on success, 0 is not returned
>>>   * on error, if add_page_for_migratioin() return 1, and the following err1
>>>     from do_move_pages_to_node() is set, the err1 is not returned since err
>>>     is 1
>>>
>>> And these behaviors break the user interface.
>>>
>>> Fixes: e0153fc2c760 ("mm: move_pages: return valid node id in status if the
>>> page is already on the target node").

The Fixes tag should be different, right? Because I don't think that
commit introduced this problem.

thanks,
--
John Hubbard
NVIDIA

>>> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
>>>
>>> ---
>>> v2:
>>>   * put more words to explain the error case
>>> ---
>>> mm/migrate.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>> index 86873b6f38a7..430fdccc733e 100644
>>> --- a/mm/migrate.c
>>> +++ b/mm/migrate.c
>>> @@ -1676,7 +1676,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>>> 	err1 = do_move_pages_to_node(mm, &pagelist, current_node);
>>> 	if (!err1)
>>> 		err1 = store_status(status, start, current_node, i - start);
>>> -	if (!err)
>>> +	if (err >= 0)
>>> 		err = err1;
>>
>> Ok, as mentioned by Yang and Michal, only err == 0 means no error.
>>
>> Sounds this regression should be fixed in another place. Let me send out
>> another patch.
>>
> 
> Hmm... I took another look into the case, this fix should work.
> 
> But yes, the semantic here is a little confusion. Look forward your comments
> here.
> 
>>> out:
>>> 	return err;
>>> -- 
>>> 2.17.1
>>
>> -- 
>> Wei Yang
>> Help you, Help me
> 

thanks,
-- 
John Hubbard
NVIDIA