linux-kernel - Re: [PATCH] mm/gup.c: Fix return value for __gup_longterm

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Message-ID: <7398324a-2134-3501-ca81-67a56a4c8629@nvidia.com>
Date:   Sun, 21 Aug 2022 17:14:01 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Shigeru Yoshida <syoshida@...hat.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Alistair Popple <apopple@...dia.com>,
        syzbot+616ff0452fec30f4dcfd@...kaller.appspotmail.com
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 <apopple@...dia.com>
> Reported-by: syzbot+616ff0452fec30f4dcfd@...kaller.appspotmail.com
> Signed-off-by: Shigeru Yoshida <syoshida@...hat.com>
> ---
>   mm/gup.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)

Reviewed-by: John Hubbard <jhubbard@...dia.com>

(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