From bdd0d69a32c2aa6437d23e35acc705758b835a75 Mon Sep 17 00:00:00 2001 From: Zi Yan Date: Wed, 26 Nov 2025 16:06:15 -0500 Subject: mm/huge_memory: change folio_split_supported() to folio_check_splittable() Patch series "Improve folio split related functions", v4. This patchset improves several folio split related functions to avoid future misuse. The changes are: 1. Consolidated folio splittable checks by moving truncated folio check, huge zero folio check, and writeback folio check into folio_split_supported(). Changed the function return type. Renamed it to folio_check_splittable() for clarification. 2. Replaced can_split_folio() with open coded folio_expected_ref_count() and folio_ref_count() and introduced folio_cache_ref_count(). 3. Changed min_order_for_split() to always return an order. 4. Fixed folio split stats counting. Motivation ========== This is based on Wei's observation[1] and solves several potential issues: 1. Dereferencing NULL folio->mapping in try_folio_split_to_order() if it is called on truncated folios. 2. Not handling of negative return value of min_order_for_split() in mm/memory-failure.c There is no bug in the current code. This patch (of 4): folio_split_supported() used in try_folio_split_to_order() requires folio->mapping to be non NULL, but current try_folio_split_to_order() does not check it. There is no issue in the current code, since try_folio_split_to_order() is only used in truncate_inode_partial_folio(), where folio->mapping is not NULL. To prevent future misuse, move folio->mapping NULL check (i.e., folio is truncated) into folio_split_supported(). Since folio->mapping NULL check returns -EBUSY and folio_split_supported() == false means -EINVAL, change folio_split_supported() return type from bool to int and return error numbers accordingly. Rename folio_split_supported() to folio_check_splittable() to match the return type change. While at it, move is_huge_zero_folio() check and folio_test_writeback() check into folio_check_splittable() and add kernel-doc. Remove all warnings inside folio_check_splittable() and give warnings in __folio_split() instead, so that bool warns parameter can be removed. Link: https://lkml.kernel.org/r/20251126210618.1971206-1-ziy@nvidia.com Link: https://lkml.kernel.org/r/20251126210618.1971206-2-ziy@nvidia.com Signed-off-by: Zi Yan Reviewed-by: Wei Yang Acked-by: Balbir Singh Acked-by: David Hildenbrand (Red Hat) Cc: Baolin Wang Cc: Barry Song Cc: Dev Jain Cc: Lance Yang Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Miaohe Lin Cc: Naoya Horiguchi Cc: Nico Pache Cc: Ryan Roberts Signed-off-by: Andrew Morton --- include/linux/huge_mm.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 1d439de1ca2c..66105a90b4c3 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -375,8 +375,8 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list int folio_split_unmapped(struct folio *folio, unsigned int new_order); int min_order_for_split(struct folio *folio); int split_folio_to_list(struct folio *folio, struct list_head *list); -bool folio_split_supported(struct folio *folio, unsigned int new_order, - enum split_type split_type, bool warns); +int folio_check_splittable(struct folio *folio, unsigned int new_order, + enum split_type split_type); int folio_split(struct folio *folio, unsigned int new_order, struct page *page, struct list_head *list); @@ -407,7 +407,7 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o static inline int try_folio_split_to_order(struct folio *folio, struct page *page, unsigned int new_order) { - if (!folio_split_supported(folio, new_order, SPLIT_TYPE_NON_UNIFORM, /* warns= */ false)) + if (folio_check_splittable(folio, new_order, SPLIT_TYPE_NON_UNIFORM)) return split_huge_page_to_order(&folio->page, new_order); return folio_split(folio, new_order, page, NULL); } -- cgit v1.2.3