Re: [PATCH 12/16] mm/migration: fix potential page refcounts leak in migrate_pages

[Baolin Wang]

On 3/7/2022 1:02 PM, Huang, Ying wrote:
> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
>
> > Hi Miaohe,
> >
> > On 3/4/2022 5:34 PM, Miaohe Lin wrote:
> > > In -ENOMEM case, there might be some subpages of fail-to-migrate THPs
> > > left in thp_split_pages list. We should move them back to migration
> > > list so that they could be put back to the right list by the caller
> > > otherwise the page refcnt will be leaked here. Also adjust nr_failed
> > > and nr_thp_failed accordingly to make vm events account more accurate.
> > > Fixes: b5bade978e9b ("mm: migrate: fix the return value of
> > > migrate_pages()")
> > > Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> > > ---
> > >    mm/migrate.c | 9 +++++++++
> > >    1 file changed, 9 insertions(+)
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index e0db06927f02..6c2dfed2ddb8 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -1422,6 +1422,15 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> > >    				}
> > >      				nr_failed_pages += nr_subpages;
> > > +				/*
> > > +				 * There might be some subpages of fail-to-migrate THPs
> > > +				 * left in thp_split_pages list. Move them back to migration
> > > +				 * list so that they could be put back to the right list by
> > > +				 * the caller otherwise the page refcnt will be leaked.
> > > +				 */
> > > +				list_splice_init(&thp_split_pages, from);
> > > +				nr_failed += retry;
> > > +				nr_thp_failed += thp_retry;
> >
> > Yes, I think we missed this case before, and your patch looks
> > right. But we should also update the 'rc' to return the correct number
> > of pages that were not migrated, right?
>
> Per my understanding, -ENOMEM should be returned to indicate an fatal
> error.

Ah, right. Sorry for noise.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>