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

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Message-ID: <20200122004222.GD11409@richard>
Date:   Wed, 22 Jan 2020 08:42:22 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        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 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().

>
>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

-- 
Wei Yang
Help you, Help me