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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: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yury Norov 2022-05-09 18:20:47 -07:00 committed by akpm
parent bff9beaa2e
commit 0768c8de1b
1 changed files with 17 additions and 4 deletions
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21
mm/gup.c
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@ -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);
}