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

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Message-ID: <20200121015326.GE1567@richard>
Date:   Tue, 21 Jan 2020 09:53:26 +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 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.

> out:
> 	return err;
>-- 
>2.17.1

-- 
Wei Yang
Help you, Help me