From 7fb0728a9b005b8fc55e835529047cca15191031 Mon Sep 17 00:00:00 2001 From: Mike Kravetz Date: Fri, 18 Nov 2022 11:52:49 -0800 Subject: [PATCH] hugetlb: fix __prep_compound_gigantic_page page flag setting Commit 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages") changed the order page flags were cleared and set in the head page. It moved the __ClearPageReserved after __SetPageHead. However, there is a check to make sure __ClearPageReserved is never done on a head page. If CONFIG_DEBUG_VM_PGFLAGS is enabled, the following BUG will be hit when creating a hugetlb gigantic page: page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page)) ------------[ cut here ]------------ kernel BUG at include/linux/page-flags.h:500! Call Trace will differ depending on whether hugetlb page is created at boot time or run time. Make sure to __ClearPageReserved BEFORE __SetPageHead. Link: https://lkml.kernel.org/r/20221118195249.178319-1-mike.kravetz@oracle.com Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages") Signed-off-by: Mike Kravetz Reported-by: Aneesh Kumar K.V Acked-by: Muchun Song Tested-by: Tarun Sahu Reviewed-by: Miaohe Lin Cc: Joao Martins Cc: Matthew Wilcox Cc: Michal Hocko Cc: Naoya Horiguchi Cc: Oscar Salvador Cc: Peter Xu Cc: Sidhartha Kumar Signed-off-by: Andrew Morton --- mm/hugetlb.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index e48f8ef45b17..f1385c3b6c96 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1800,6 +1800,7 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order, /* we rely on prep_new_huge_page to set the destructor */ set_compound_order(page, order); + __ClearPageReserved(page); __SetPageHead(page); for (i = 0; i < nr_pages; i++) { p = nth_page(page, i); @@ -1816,7 +1817,8 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order, * on the head page when they need know if put_page() is needed * after get_user_pages(). */ - __ClearPageReserved(p); + if (i != 0) /* head page cleared above */ + __ClearPageReserved(p); /* * Subtle and very unlikely *