From: Zi Yan Date: Fri, 17 Oct 2025 01:36:30 +0000 (-0400) Subject: mm/huge_memory: do not change split_huge_page*() target order silently X-Git-Tag: v6.12.59~7 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6393d21c6af66d517063ac98304b9fcbec30eb12;p=thirdparty%2Fkernel%2Fstable.git mm/huge_memory: do not change split_huge_page*() target order silently commit 77008e1b2ef73249bceb078a321a3ff6bc087afb upstream. Page cache folios from a file system that support large block size (LBS) can have minimal folio order greater than 0, thus a high order folio might not be able to be split down to order-0. Commit e220917fa507 ("mm: split a folio in minimum folio order chunks") bumps the target order of split_huge_page*() to the minimum allowed order when splitting a LBS folio. This causes confusion for some split_huge_page*() callers like memory failure handling code, since they expect after-split folios all have order-0 when split succeeds but in reality get min_order_for_split() order folios and give warnings. Fix it by failing a split if the folio cannot be split to the target order. Rename try_folio_split() to try_folio_split_to_order() to reflect the added new_order parameter. Remove its unused list parameter. [The test poisons LBS folios, which cannot be split to order-0 folios, and also tries to poison all memory. The non split LBS folios take more memory than the test anticipated, leading to OOM. The patch fixed the kernel warning and the test needs some change to avoid OOM.] Link: https://lkml.kernel.org/r/20251017013630.139907-1-ziy@nvidia.com Fixes: e220917fa507 ("mm: split a folio in minimum folio order chunks") Signed-off-by: Zi Yan Reported-by: syzbot+e6367ea2fdab6ed46056@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68d2c943.a70a0220.1b52b.02b3.GAE@google.com/ Reviewed-by: Luis Chamberlain Reviewed-by: Pankaj Raghav Reviewed-by: Wei Yang Acked-by: David Hildenbrand Reviewed-by: Lorenzo Stoakes Reviewed-by: Miaohe Lin Cc: Baolin Wang Cc: Barry Song Cc: David Hildenbrand Cc: Dev Jain Cc: Jane Chu Cc: Lance Yang Cc: Liam Howlett Cc: Mariano Pache Cc: Matthew Wilcox (Oracle) Cc: Naoya Horiguchi Cc: Ryan Roberts Cc: Christian Brauner Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index ef5b80e48599c..f70b048596b53 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -353,20 +353,7 @@ int min_order_for_split(struct folio *folio); int split_folio_to_list(struct folio *folio, struct list_head *list); static inline int split_huge_page(struct page *page) { - struct folio *folio = page_folio(page); - int ret = min_order_for_split(folio); - - if (ret < 0) - return ret; - - /* - * split_huge_page() locks the page before splitting and - * expects the same page that has been split to be locked when - * returned. split_folio(page_folio(page)) cannot be used here - * because it converts the page to folio and passes the head - * page to be split. - */ - return split_huge_page_to_list_to_order(page, NULL, ret); + return split_huge_page_to_list_to_order(page, NULL, 0); } void deferred_split_folio(struct folio *folio, bool partially_mapped); @@ -538,6 +525,12 @@ static inline int split_huge_page(struct page *page) return 0; } +static inline int min_order_for_split(struct folio *folio) +{ + VM_WARN_ON_ONCE_FOLIO(1, folio); + return -EINVAL; +} + static inline int split_folio_to_list(struct folio *folio, struct list_head *list) { return 0; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 92df29fc44fdc..0bb0ce0c106b0 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3597,12 +3597,7 @@ int min_order_for_split(struct folio *folio) int split_folio_to_list(struct folio *folio, struct list_head *list) { - int ret = min_order_for_split(folio); - - if (ret < 0) - return ret; - - return split_huge_page_to_list_to_order(&folio->page, list, ret); + return split_huge_page_to_list_to_order(&folio->page, list, 0); } /*