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.
[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 ziy@nvidia.com Reported-by: syzbot+e6367ea2fdab6ed46056@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68d2c943.a70a0220.1b52b.02b3.GAE@google.com/ Reviewed-by: Luis Chamberlain mcgrof@kernel.org Reviewed-by: Pankaj Raghav p.raghav@samsung.com Reviewed-by: Wei Yang richard.weiyang@gmail.com Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Reviewed-by: Miaohe Lin linmiaohe@huawei.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Barry Song baohua@kernel.org Cc: David Hildenbrand david@redhat.com Cc: Dev Jain dev.jain@arm.com Cc: Jane Chu jane.chu@oracle.com Cc: Lance Yang lance.yang@linux.dev Cc: Liam Howlett liam.howlett@oracle.com Cc: Mariano Pache npache@redhat.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Naoya Horiguchi nao.horiguchi@gmail.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: Christian Brauner brauner@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit 77008e1b2ef73249bceb078a321a3ff6bc087afb) --- include/linux/huge_mm.h | 21 +++++++-------------- mm/huge_memory.c | 7 +------ 2 files changed, 8 insertions(+), 20 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index ef5b80e48599..f70b048596b5 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 92df29fc44fd..0bb0ce0c106b 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); }
/*