Re: [PATCH rc] mm/gup: use unpin_user_pages() in check_and_migrate_cma_pages()

[Ira Weiny <ira.weiny@intel.com>]

On Fri, Oct 30, 2020 at 01:32:28PM -0300, 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.
> 
> Cc: <stable@kernel.org>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages")
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  mm/gup.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> I don't have any way to test CMA stuff, this was noticed by inspection.
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 1bb349e5ed212a..2e26757f3c9276 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1630,8 +1630,11 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm,
>  		/*
>  		 * drop the above get_user_pages reference.
>  		 */

I wonder if that comment should be deleted/modified?  It does not seem to apply
any longer.

Also, looks like there is another place this occurs right before the call to
check_and_migrate_cma_pages() in __gup_longterm_locked()

1730                 if (check_dax_vmas(vmas_tmp, rc)) {
1731                         for (i = 0; i < rc; i++)
1732                                 put_page(pages[i]);
1733                         rc = -EOPNOTSUPP;
1734                         goto out;
1735                 }

We should change that site as well.

And since we now have 2 places should this be a helper?

Ira

> -		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)) {
> -- 
> 2.28.0
>