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

David Hildenbrand
2022-11-28T08:20:01Z

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@xs4all.nl>
>>> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
>>> Cc: Tomasz Figa <tfiga@chromium.org>
>>> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
>>> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>   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