2020-05-22 01:07:13

by John Hubbard

Subject: [PATCH] mm/gup: might_lock_read(mmap_sem) in get_user_pages_fast()

Instead of scattering these assertions across the drivers,
do this assertion inside the core of get_user_pages_fast*()
functions. That also includes pin_user_pages_fast*()
routines.

Add a might_lock_read(mmap_sem) call to internal_get_user_pages_fast().

Suggested-by: Matthew Wilcox <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Signed-off-by: John Hubbard <[email protected]>
---

Hi Andrew,

This applies on top of [1], which in turn applies to
today's (20200521) linux-next.

As noted in the discussion [2], this will need changing from
mmap_sem to mmap_lock, after Michel Lespinasse's patchset
arrives.

[1]
https://lore.kernel.org/r/[email protected]

[2] https://lore.kernel.org/linux-mm/[email protected]/

thanks,
John Hubbard
NVIDIA

mm/gup.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index ada6aa79576dc..3462c076e8ecf 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2728,6 +2728,9 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
FOLL_FAST_ONLY)))
return -EINVAL;

+ if (!(gup_flags & FOLL_FAST_ONLY))
+ might_lock_read(&current->mm->mmap_sem);
+
start = untagged_addr(start) & PAGE_MASK;
addr = start;
len = (unsigned long) nr_pages << PAGE_SHIFT;
--
2.26.2

2020-05-22 01:20:57

by Matthew Wilcox

Subject: Re: [PATCH] mm/gup: might_lock_read(mmap_sem) in get_user_pages_fast()

On Thu, May 21, 2020 at 06:04:43PM -0700, John Hubbard wrote:
> Instead of scattering these assertions across the drivers,
> do this assertion inside the core of get_user_pages_fast*()
> functions. That also includes pin_user_pages_fast*()
> routines.
>
> Add a might_lock_read(mmap_sem) call to internal_get_user_pages_fast().
>
> Suggested-by: Matthew Wilcox <[email protected]>

Yup, this is exactly what I meant. Feel free to transform this into
an Acked-by: or Reviewed-by: if that's the appropriate tag.

Thanks, John!