Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [Patch v2] mm/migrate.c: also overwrite error when it is bigger
 than zero
To:     Wei Yang <richardw.yang@linux.intel.com>
CC:     <akpm@linux-foundation.org>, <yang.shi@linux.alibaba.com>,
        <vbabka@suse.cz>, <cl@linux.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <mhocko@kernel.org>
References: <20200119065753.21694-1-richardw.yang@linux.intel.com>
 <20200121015326.GE1567@richard> <20200121023408.GA3636@richard>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <0aa42c19-4144-5c7a-10f5-162b1b068d4c@nvidia.com>
Date:   Tue, 21 Jan 2020 11:33:16 -0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0)
 Gecko/20100101 Thunderbird/68.4.1
MIME-Version: 1.0
In-Reply-To: <20200121023408.GA3636@richard>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@linux.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