Hi David, Tomasz, On 16/11/2022 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. I've decided to revert 707947247e95: I have not been able to reproduce the problem described in that commit, and Tomasz reported that it caused problems with a specific use-case they encountered. I'll post that patch soon and I expect it to land in 6.2. It will cause a conflict with this patch, though. If the problem described in that patch occurs again, then I will revisit it and hopefully do a better job than I did before. That commit was not my finest moment. Regards, Hans > > 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;