On 10/2/20 10:53 AM, Daniel Vetter wrote:
For $reasons I've stumbled over this code and I'm not sure the change
to the new gup functions in 55a650c35fea ("mm/gup: frame_vector:
convert get_user_pages() --> pin_user_pages()") was entirely correct.
This here is used for long term buffers (not just quick I/O) like
RDMA, and John notes this in his patch. But I thought the rule for
these is that they need to add FOLL_LONGTERM, which John's patch
didn't do.
Yep. The earlier gup --> pup conversion patches were intended to not
have any noticeable behavior changes, and FOLL_LONGTERM, with it's
special cases and such, added some risk that I wasn't ready to take
on yet. Also, FOLL_LONGTERM rules are only *recently* getting firmed
up. So there was some doubt at least in my mind, about which sites
should have it.
But now that we're here, I think it's really good that you've brought
this up. It's definitely time to add FOLL_LONGTERM wherever it's missing.
thanks,
--
John Hubbard
NVIDIA
There is already a dax specific check (added in b7f0554a56f2 ("mm:
fail get_vaddr_frames() for filesystem-dax mappings")), so this seems
like the prudent thing to do.
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-samsung-soc@xxxxxxxxxxxxxxx
Cc: linux-media@xxxxxxxxxxxxxxx
---
Hi all,
I stumbled over this and figured typing this patch can't hurt. Really
just to maybe learn a few things about how gup/pup is supposed to be
used (we have a bit of that in drivers/gpu), this here isn't really
ralated to anything I'm doing.
I'm also wondering whether the explicit dax check should be removed,
since FOLL_LONGTERM should take care of that already.
-Daniel
---
mm/frame_vector.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 5d34c9047e9c..3507e09cb3ff 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -35,7 +35,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
- unsigned int gup_flags = FOLL_WRITE | FOLL_FORCE;
+ unsigned int gup_flags = FOLL_WRITE | FOLL_FORCE | FOLL_LONGTERM;
int ret = 0;
int err;
int locked;
