Re: [PATCH mm-unstable v1 16/20] mm/frame-vector: remove FOLL_FORCE usage

[David Hildenbrand]

On 28.11.22 09:17, Hans Verkuil wrote:
> Hi David,
>
> On 27/11/2022 11:35, David Hildenbrand wrote:
> > On 16.11.22 11:26, David Hildenbrand wrote:
> > > FOLL_FORCE is really only for ptrace access. According to commit
> > > 707947247e95 ("media: videobuf2-vmalloc: get_userptr: buffers are always
> > > writable"), get_vaddr_frames() currently pins all pages writable as a
> > > workaround for issues with read-only buffers.
> > >
> > > FOLL_FORCE, however, seems to be a legacy leftover as it predates
> > > commit 707947247e95 ("media: videobuf2-vmalloc: get_userptr: buffers are
> > > always writable"). Let's just remove it.
> > >
> > > Once the read-only buffer issue has been resolved, FOLL_WRITE could
> > > again be set depending on the DMA direction.
> > >
> > > Cc: Hans Verkuil <hverkuil@xxxxxxxxx>
> > > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > > Cc: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> > > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > > Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> > > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> > > ---
> > >    drivers/media/common/videobuf2/frame_vector.c | 2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c
> > > index 542dde9d2609..062e98148c53 100644
> > > --- a/drivers/media/common/videobuf2/frame_vector.c
> > > +++ b/drivers/media/common/videobuf2/frame_vector.c
> > > @@ -50,7 +50,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> > >        start = untagged_addr(start);
> > >          ret = pin_user_pages_fast(start, nr_frames,
> > > -                  FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
> > > +                  FOLL_WRITE | FOLL_LONGTERM,
> > >                      (struct page **)(vec->ptrs));
> > >        if (ret > 0) {
> > >            vec->got_ref = true;
> >
> >
> > Hi Andrew,
> >
> > see the discussion at [1] regarding a conflict and how to proceed with
> > upstreaming. The conflict would be easy to resolve, however, also
> > the patch description doesn't make sense anymore with [1].
>
> Might it be easier and less confusing if you post a v2 of this series
> with my patch first? That way it is clear that 1) my patch has to come
> first, and 2) that it is part of a single series and should be merged
> by the mm subsystem.
>
> Less chances of things going wrong that way.
>
> Just mention in the v2 cover letter that the first patch was added to
> make it easy to backport that fix without being hampered by merge
> conflicts if it was added after your frame_vector.c patch.

Yes, that's the way I would naturally do, it, however, Andrew prefers 
delta updates for minor changes.

@Andrew, whatever you prefer!

Thanks!

--
Thanks,

David / dhildenb