From: Yury Norov Subject: 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) Reviewed-by: John Hubbard Cc: Minchan Kim Signed-off-by: Andrew Morton --- mm/gup.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) --- a/mm/gup.c~mm-gup-fix-comments-to-pin_user_pages_ +++ a/mm/gup.c @@ -2969,6 +2969,9 @@ int pin_user_pages_fast(unsigned long st 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 lo */ 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_on * @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_str 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, 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 lo 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); } _