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

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Message-ID: <9acef3fe-4c9a-6ecb-daa0-767d98f572ae@nvidia.com>
Date:   Tue, 21 Jan 2020 17:29:50 -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 1/21/20 4:42 PM, Wei Yang wrote:
> On Tue, Jan 21, 2020 at 11:33:16AM -0800, John Hubbard wrote:
>> 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.
> 
> This is the correct one.
> 
> Before this, we don't return 1 from add_page_for_migration().
> 

OK, then. :)

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
>