diff mbox series

[v2] mm/gup: fix comments to pin_user_pages_*()

Message ID 20220422015839.1274328-1-yury.norov@gmail.com (mailing list archive)
State New
Headers show
Series [v2] mm/gup: fix comments to pin_user_pages_*() | expand

Commit Message

Yury Norov April 22, 2022, 1:58 a.m. UTC 
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/

CC: Minchan Kim <minchan@kernel.org>
CC: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
---

v1: https://lore.kernel.org/linux-mm/92a2715c-3c98-251d-9195-872d1cf01f9d@nvidia.com/#t
v2: Remove comment for WARN_ON_ONCE() and reword commit message.
  
 mm/gup.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

Comments

John Hubbard April 22, 2022, 5:56 a.m. UTC | #1 
On 4/21/22 18:58, Yury Norov wrote:
> 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/
> 
> CC: Minchan Kim <minchan@kernel.org>
> CC: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
> ---

Looks good. Please feel free to add:

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


thanks,
diff mbox series

Patch

diff --git a/mm/gup.c b/mm/gup.c
index f598a037eb04..b1e96b6192de 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2871,6 +2871,9 @@  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);
 }
@@ -2893,6 +2896,9 @@  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.
@@ -2920,8 +2926,7 @@  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
@@ -2944,6 +2949,9 @@  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);
@@ -2957,8 +2965,7 @@  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.
  *
@@ -2976,6 +2983,9 @@  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);
@@ -2994,6 +3004,9 @@  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);
 }