2022-04-22 05:52:56

by Yury Norov

Subject: [PATCH v2] 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/[email protected]/

CC: Minchan Kim <[email protected]>
CC: John Hubbard <[email protected]>
Signed-off-by: Yury Norov (NVIDIA) <[email protected]>
---

v1: https://lore.kernel.org/linux-mm/[email protected]/#t
v2: Remove comment for WARN_ON_ONCE() and reword commit message.

mm/gup.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)

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);
}
--
2.32.0

2022-04-22 20:23:14

by John Hubbard

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

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/[email protected]/
>
> CC: Minchan Kim <[email protected]>
> CC: John Hubbard <[email protected]>
> Signed-off-by: Yury Norov (NVIDIA) <[email protected]>
> ---

Looks good. Please feel free to add:

Reviewed-by: John Hubbard <[email protected]>


thanks,
--
John Hubbard
NVIDIA

>
> v1: https://lore.kernel.org/linux-mm/[email protected]/#t
> v2: Remove comment for WARN_ON_ONCE() and reword commit message.
>
> mm/gup.c | 21 +++++++++++++++++----
> 1 file changed, 17 insertions(+), 4 deletions(-)
>
> 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);
> }