2022-08-21 18:42:52

by Shigeru Yoshida

Subject: [PATCH] mm/gup.c: Fix return value for __gup_longterm_locked()

__get_user_pages_locked() may return the number of pages less than
nr_pages. So __gup_longterm_locked() have to return the number of
pages __get_user_pages_locked() returns if it succeeded, not nr_pages
passed.

Fixes: 61c63c2076d9 (mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes)
CC: Alistair Popple <[email protected]>
Reported-by: [email protected]
Signed-off-by: Shigeru Yoshida <[email protected]>
---
mm/gup.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 5aa7531a703b..542cf74c59b0 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2068,22 +2068,22 @@ static long __gup_longterm_locked(struct mm_struct *mm,
unsigned int gup_flags)
{
unsigned int flags;
- long rc;
+ long rc, nr_pinned_pages;

if (!(gup_flags & FOLL_LONGTERM))
return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
NULL, gup_flags);
flags = memalloc_pin_save();
do {
- rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
- NULL, gup_flags);
- if (rc <= 0)
+ nr_pinned_pages = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
+ NULL, gup_flags);
+ if (nr_pinned_pages <= 0)
break;
- rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
+ rc = check_and_migrate_movable_pages(nr_pinned_pages, pages, gup_flags);
} while (rc == -EAGAIN);
memalloc_pin_restore(flags);

- return rc ? rc : nr_pages;
+ return rc ? rc : nr_pinned_pages;
}

static bool is_valid_gup_flags(unsigned int gup_flags)
--
2.37.2

2022-08-22 00:34:11

by John Hubbard

Subject: Re: [PATCH] mm/gup.c: Fix return value for __gup_longterm_locked()

On 8/21/22 11:35, Shigeru Yoshida wrote:
> __get_user_pages_locked() may return the number of pages less than
> nr_pages. So __gup_longterm_locked() have to return the number of
> pages __get_user_pages_locked() returns if it succeeded, not nr_pages
> passed.

s/passed/requested/

>
> Fixes: 61c63c2076d9 (mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes)
> CC: Alistair Popple <[email protected]>
> Reported-by: [email protected]
> Signed-off-by: Shigeru Yoshida <[email protected]>
> ---
> mm/gup.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)

Reviewed-by: John Hubbard <[email protected]>

(with a couple of nits about line length, below)

>
> diff --git a/mm/gup.c b/mm/gup.c
> index 5aa7531a703b..542cf74c59b0 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2068,22 +2068,22 @@ static long __gup_longterm_locked(struct mm_struct *mm,
> unsigned int gup_flags)
> {
> unsigned int flags;
> - long rc;
> + long rc, nr_pinned_pages;
>
> if (!(gup_flags & FOLL_LONGTERM))
> return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
> NULL, gup_flags);
> flags = memalloc_pin_save();
> do {
> - rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
> - NULL, gup_flags);
> - if (rc <= 0)
> + nr_pinned_pages = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
> + NULL, gup_flags);

Can you please wrap at 80 cols, though?

> + if (nr_pinned_pages <= 0)
> break;
> - rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
> + rc = check_and_migrate_movable_pages(nr_pinned_pages, pages, gup_flags);

Also here.

> } while (rc == -EAGAIN);
> memalloc_pin_restore(flags);
>
> - return rc ? rc : nr_pages;
> + return rc ? rc : nr_pinned_pages;
> }
>
> static bool is_valid_gup_flags(unsigned int gup_flags)

thanks,
--
John Hubbard
NVIDIA