2020-09-30 01:22:35

by Jann Horn

Subject: [PATCH 4/4] mm/gup: Assert that the mmap lock is held in __get_user_pages()

After having cleaned up all GUP callers (except for the atomisp staging
driver, which currently gets mmap locking completely wrong [1]) to always
ensure that they hold the mmap lock when calling into GUP (unless the mm is
not yet globally visible), add an assertion to make sure it stays that way
going forward.

[1] https://lore.kernel.org/lkml/CAG48ez3tZAb9JVhw4T5e-i=h2_DUZxfNRTDsagSRCVazNXx5qA@mail.gmail.com/

Signed-off-by: Jann Horn <[email protected]>
---
mm/gup.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index f11d39867cf5..3e5d843215b9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1020,6 +1020,8 @@ static long __get_user_pages(struct mm_struct *mm,
struct vm_area_struct *vma = NULL;
struct follow_page_context ctx = { NULL };

+ mmap_assert_locked(mm);
+
if (!nr_pages)
return 0;

--
2.28.0.709.gb0816b6eb0-goog

2020-09-30 12:36:02

by Jason Gunthorpe

Subject: Re: [PATCH 4/4] mm/gup: Assert that the mmap lock is held in __get_user_pages()

On Tue, Sep 29, 2020 at 06:20:01PM -0700, Jann Horn wrote:
> After having cleaned up all GUP callers (except for the atomisp staging
> driver, which currently gets mmap locking completely wrong [1]) to always
> ensure that they hold the mmap lock when calling into GUP (unless the mm is
> not yet globally visible), add an assertion to make sure it stays that way
> going forward.
>
> [1] https://lore.kernel.org/lkml/CAG48ez3tZAb9JVhw4T5e-i=h2_DUZxfNRTDsagSRCVazNXx5qA@mail.gmail.com/
>
> Signed-off-by: Jann Horn <[email protected]>
> ---
> mm/gup.c | 2 ++
> 1 file changed, 2 insertions(+)

I'm happy to see this, I have observed many cases of missing locking
here.

Reviewed-by: Jason Gunthorpe <[email protected]>

Thanks,
Jason

2020-10-01 01:07:44

by Michel Lespinasse

Subject: Re: [PATCH 4/4] mm/gup: Assert that the mmap lock is held in __get_user_pages()

On Wed, Sep 30, 2020 at 5:32 AM Jason Gunthorpe <[email protected]> wrote:
> On Tue, Sep 29, 2020 at 06:20:01PM -0700, Jann Horn wrote:
> > After having cleaned up all GUP callers (except for the atomisp staging
> > driver, which currently gets mmap locking completely wrong [1]) to always
> > ensure that they hold the mmap lock when calling into GUP (unless the mm is
> > not yet globally visible), add an assertion to make sure it stays that way
> > going forward.

Thanks for doing this, there is a lot of value in ensuring that a
function's callers follows the prerequisites.

Acked-by: Michel Lespinasse <[email protected]>