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

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Oct 30, 2020 at 01:50:26PM -0700, Ira Weiny wrote:
> 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
> > +++ 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.

It is still basically right, the 'above' is just a bit vauge.. Don't
want to touch extra stuff for a stable patch.

> 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                 }

Oh, yes! I will update this in v2 - good eyes
 
> And since we now have 2 places should this be a helper?

I have another patch that deletes check_dax_vmas() and this code

https://github.com/jgunthorpe/linux/commit/48ee608271e124e4a89353b9694502372c1b2df0

Does it look OK to you? I was going to check it again and post next
week

Thus for this stable patch let's just leave it simple?

Thanks,
Jason