On Mon, Nov 02, 2020 at 02:19:59PM -0400, Jason Gunthorpe wrote:
> When FOLL_PIN is passed to __get_user_pages() the page list must be put
> back using unpin_user_pages() otherwise the page pin reference persists in
> a corrupted state.
>
> There are two places in the unwind of __gup_longterm_locked() that put the
> pages back without checking. Normally on error this function would return
> the partial page list making this the caller's responsibility, but in
> these two cases the caller is not allowed to see these pages at all.
>
> Cc: <stable@xxxxxxxxxx>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages")
> Reported-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> ---
> mm/gup.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> v2:
> - Catch the DAX related case as well (Ira)
> v1: https://lore.kernel.org/r/0-v1-976effcd4468+d4-gup_cma_fix_jgg@xxxxxxxxxx
>
> Andrew, this version with a modified commit message and extra hunk replaces:
> mm-gup-use-unpin_user_pages-in-check_and_migrate_cma_pages.patch
>
> Thanks,
> Jason
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 102877ed77a4b4..98eb8e6d2609c3 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1647,8 +1647,11 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
> /*
> * drop the above get_user_pages reference.
> */
> - for (i = 0; i < nr_pages; i++)
> - put_page(pages[i]);
> + if (gup_flags & FOLL_PIN)
> + unpin_user_pages(pages, nr_pages);
> + else
> + for (i = 0; i < nr_pages; i++)
> + put_page(pages[i]);
>
> if (migrate_pages(&cma_page_list, alloc_migration_target, NULL,
> (unsigned long)&mtc, MIGRATE_SYNC, MR_CONTIG_RANGE)) {
> @@ -1728,8 +1731,11 @@ static long __gup_longterm_locked(struct mm_struct *mm,
> goto out;
>
> if (check_dax_vmas(vmas_tmp, rc)) {
> - for (i = 0; i < rc; i++)
> - put_page(pages[i]);
> + if (gup_flags & FOLL_PIN)
> + unpin_user_pages(pages, rc);
> + else
> + for (i = 0; i < rc; i++)
> + put_page(pages[i]);
> rc = -EOPNOTSUPP;
> goto out;
> }
> --
> 2.28.0
>
