linux-kernel - Re: [PATCH v2] mm: gup: fix comment of __get_user

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Date:   Mon, 28 Oct 2019 11:50:31 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Liu Xiang <liuxiang_1999@....com>, <linux-mm@...ck.org>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm: gup: fix comment of __get_user_pages()

On 10/24/19 8:04 AM, Liu Xiang wrote:
> Fix comment of __get_user_pages() and make it more clear.
> 
> Suggested-by: John Hubbard <jhubbard@...dia.com>
> Signed-off-by: Liu Xiang <liuxiang_1999@....com>
> ---
> 
> Changes in v2:
>  as suggested by John, rewrite the comment about return value.
> 
>  mm/gup.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 8f236a3..bc6a254 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -734,11 +734,17 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
>   *		Or NULL if the caller does not require them.
>   * @nonblocking: whether waiting for disk IO or mmap_sem contention
>   *
> - * Returns number of pages pinned. This may be fewer than the number
> - * requested. If nr_pages is 0 or negative, returns 0. If no pages
> - * were pinned, returns -errno. Each page returned must be released
> - * with a put_page() call when it is finished with. vmas will only
> - * remain valid while mmap_sem is held.
> + * Returns either number of pages pinned (which may be less than the
> + * number requested), or an error. Details about the return value:
> + *
> + * -- If nr_pages is 0, returns 0.
> + * -- If nr_pages is >0, but no pages were pinned, returns -errno.
> + * -- If nr_pages is >0, and some pages were pinned, returns the number of
> + *    pages pinned. Again, this may be less than nr_pages.
> + *
> + * The caller is responsible for releasing returned @pages, via put_page().
> + *
> + * @vmas are valid only as long as mmap_sem is held.

Just remembered: this identical paragraph is also written in the 
get_user_pages_remote() comments. It would be ideal to apply the same fix to 
that identical blob of text.


thanks,
-- 
John Hubbard
NVIDIA

>   *
>   * Must be called with mmap_sem held.  It may be released.  See below.
>   *
>