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

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Date:   Tue, 21 Jan 2020 10:34:08 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, yang.shi@...ux.alibaba.com,
        jhubbard@...dia.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 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").
>>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

-- 
Wei Yang
Help you, Help me