linux-kernel - Re: [PATCH 3/7] mm/gup: Fix the outdated code comments above get_user_pages

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Message-ID: <Z-qfflDA8pEn7HZ5@localhost.localdomain>
Date: Mon, 31 Mar 2025 15:58:22 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Baoquan He <bhe@...hat.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] mm/gup: Fix the outdated code comments above
 get_user_pages_unlocked()

On Sun, Mar 30, 2025 at 08:17:13PM +0800, Baoquan He wrote:
> Since commit f0818f472d8d ("mm: gup: add get_user_pages_locked
> and get_user_pages_unlocked"), get_user_pages() doesn't need to have
> mmap_lock held anymore. It calls __get_user_pages_locked() which
> can acquire and drop the mmap_lock internaly.

Yes, __get_user_pages_locked() can aquire and drop the lock, but AFAICS
get_user_pages() always calls __get_user_pages_locked() with locked=1,
which means that is holding the lock, right?

> Hence remove the incorrect code comments now.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  mm/gup.c | 16 +++-------------
>  1 file changed, 3 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 8788105daee8..3345a065c2cb 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2702,19 +2702,9 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
>  EXPORT_SYMBOL(get_user_pages);
>  
>  /*
> - * get_user_pages_unlocked() is suitable to replace the form:
> - *
> - *      mmap_read_lock(mm);
> - *      get_user_pages(mm, ..., pages, NULL);
> - *      mmap_read_unlock(mm);
> - *
> - *  with:
> - *
> - *      get_user_pages_unlocked(mm, ..., pages);
> - *
> - * It is functionally equivalent to get_user_pages_fast so
> - * get_user_pages_fast should be used instead if specific gup_flags
> - * (e.g. FOLL_FORCE) are not required.
> + * get_user_pages_unlocked() is functionally equivalent to
> + * get_user_pages_fast so get_user_pages_fast should be used instead
> + * if specific gup_flags (e.g. FOLL_FORCE) are not required.
>   */
>  long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>  			     struct page **pages, unsigned int gup_flags)
> -- 
> 2.41.0
> 
> 

-- 
Oscar Salvador
SUSE Labs