Re: [PATCH v2] mm/gup.c: Simplify and fix check_and_migrate_movable_pages() return codes

Andrew Morton
2022-08-03T00:12:21Z

On Tue, 2 Aug 2022 10:30:12 +1000 Alistair Popple <apopple@nvidia.com> wrote:

> When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages()
> is called to migrate pages out of zones which should not contain any
> longterm pinned pages.
>
> When migration succeeds all pages will have been unpinned so pinning
> needs to be retried. This is indicated by returning zero. When all pages
> are in the correct zone the number of pinned pages is returned.
>
> However migration can also fail, in which case pages are unpinned and
> -ENOMEM is returned. However if the failure was due to not being unable
> to isolate a page zero is returned. This leads to indefinite looping in
> __gup_longterm_locked().
>
> Fix this by simplifying the return codes such that zero indicates all
> pages were successfully pinned in the correct zone while errors indicate
> either pages were migrated and pinning should be retried or that
> migration has failed and therefore the pinning operation should fail.
>
> This fixes the indefinite looping on page isolation failure by failing
> the pin operation instead of retrying indefinitely.
>

Are we able to identify a Fixes: for this? Presumably something in the
series "Add MEMORY_DEVICE_COHERENT for coherent device memory mapping"?