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

[Yang Shi]

On 1/20/20 5:53 PM, 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@xxxxxxxxxxxxxxx>
> >
> > ---
> > 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.

I think Michal means do_move_pages_to_node() only, 
add_page_for_migration() returns 1 on purpose.

But, actually the syscall may still return > 0 value since err1 might be 
> 0. Anyway, this is another regression. The patch itself looks correct 
to me.

Acked-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>


> Sounds this regression should be fixed in another place. Let me send out
> another patch.
>
> > out:
> > 	return err;
> > --
> > 2.17.1