Commit 0768c8de authored by Yury Norov's avatar Yury Norov Committed by Andrew Morton
Browse files

mm/gup: fix comments to pin_user_pages_*() 

pin_user_pages API forces FOLL_PIN in gup_flags, which means that the API
requires struct page **pages to be provided (not NULL).  However, the
comment to pin_user_pages() clearly allows for passing in a NULL @pages
argument.

Remove the incorrect comments, and add WARN_ON_ONCE(!pages) calls to
enforce the API.

It has been independently spotted by Minchan Kim and confirmed with
John Hubbard:

https://lore.kernel.org/all/YgWA0ghrrzHONehH@google.com/

Link: https://lkml.kernel.org/r/20220422015839.1274328-1-yury.norov@gmail.com


Signed-off-by: default avatarYury Norov (NVIDIA) <yury.norov@gmail.com>
Reviewed-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent bff9beaa

mm/gup.c

+17 −4
Original line number Diff line number Diff line
@@ -2969,6 +2969,9 @@ int pin_user_pages_fast(unsigned long start, int nr_pages, 
	if (WARN_ON_ONCE(gup_flags & FOLL_GET))

		return -EINVAL;



	if (WARN_ON_ONCE(!pages))

		return -EINVAL;



	gup_flags |= FOLL_PIN;

	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);

}
@@ -2991,6 +2994,9 @@ int pin_user_pages_fast_only(unsigned long start, int nr_pages, 
	 */

	if (WARN_ON_ONCE(gup_flags & FOLL_GET))

		return 0;



	if (WARN_ON_ONCE(!pages))

		return 0;

	/*

	 * FOLL_FAST_ONLY is required in order to match the API description of

	 * this routine: no fall back to regular ("slow") GUP.
@@ -3018,8 +3024,7 @@ EXPORT_SYMBOL_GPL(pin_user_pages_fast_only); 
 * @nr_pages:	number of pages from start to pin

 * @gup_flags:	flags modifying lookup behaviour

 * @pages:	array that receives pointers to the pages pinned.

 *		Should be at least nr_pages long. Or NULL, if caller

 *		only intends to ensure the pages are faulted in.

 *		Should be at least nr_pages long.

 * @vmas:	array of pointers to vmas corresponding to each page.

 *		Or NULL if the caller does not require them.

 * @locked:	pointer to lock flag indicating whether lock is held and
@@ -3042,6 +3047,9 @@ long pin_user_pages_remote(struct mm_struct *mm, 
	if (WARN_ON_ONCE(gup_flags & FOLL_GET))

		return -EINVAL;



	if (WARN_ON_ONCE(!pages))

		return -EINVAL;



	gup_flags |= FOLL_PIN;

	return __get_user_pages_remote(mm, start, nr_pages, gup_flags,

				       pages, vmas, locked);
@@ -3055,8 +3063,7 @@ EXPORT_SYMBOL(pin_user_pages_remote); 
 * @nr_pages:	number of pages from start to pin

 * @gup_flags:	flags modifying lookup behaviour

 * @pages:	array that receives pointers to the pages pinned.

 *		Should be at least nr_pages long. Or NULL, if caller

 *		only intends to ensure the pages are faulted in.

 *		Should be at least nr_pages long.

 * @vmas:	array of pointers to vmas corresponding to each page.

 *		Or NULL if the caller does not require them.

 *
@@ -3074,6 +3081,9 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages, 
	if (WARN_ON_ONCE(gup_flags & FOLL_GET))

		return -EINVAL;



	if (WARN_ON_ONCE(!pages))

		return -EINVAL;



	gup_flags |= FOLL_PIN;

	return __gup_longterm_locked(current->mm, start, nr_pages,

				     pages, vmas, gup_flags);
@@ -3092,6 +3102,9 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages, 
	if (WARN_ON_ONCE(gup_flags & FOLL_GET))

		return -EINVAL;



	if (WARN_ON_ONCE(!pages))

		return -EINVAL;



	gup_flags |= FOLL_PIN;

	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);

}