[130/173] hugetlb: fix update_and_free_page contig page struct assumption

Commit Message

Andrew Morton Feb. 24, 2021, 8:07 p.m. UTC

From: Mike Kravetz <[e-mail]>
Subject: hugetlb: fix update_and_free_page contig page struct assumption

page structs are not guaranteed to be contiguous for gigantic pages.  The
routine update_and_free_page can encounter a gigantic page, yet it assumes
page structs are contiguous when setting page flags in subpages.

If update_and_free_page encounters non-contiguous page structs, we can see
“BUG: Bad page state in process …” errors.

Non-contiguous page structs are generally not an issue.  However, they can
exist with a specific kernel configuration and hotplug operations.  For
example: Configure the kernel with CONFIG_SPARSEMEM and
!CONFIG_SPARSEMEM_VMEMMAP.  Then, hotplug add memory for the area where
the gigantic page will be allocated.  Zi Yan outlined steps to reproduce
here [1].

[1] https://lore.kernel.org/linux-mm/[e-mail]/

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 944d9fec8d7a ("hugetlb: add support for gigantic page allocation at runtime")
Signed-off-by: Zi Yan <[e-mail]>
Signed-off-by: Mike Kravetz <[e-mail]>
Cc: Zi Yan <[e-mail]>
Cc: Davidlohr Bueso <[e-mail]>
Cc: "Kirill A . Shutemov" <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Joao Martins <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/hugetlb.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Patch

--- a/mm/hugetlb.c~hugetlb-fix-update_and_free_page-contig-page-struct-assumption
+++ a/mm/hugetlb.c
@@ -1321,14 +1321,16 @@  static inline void destroy_compound_giga
 static void update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
+	struct page *subpage = page;
 
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
 	h->nr_huge_pages--;
 	h->nr_huge_pages_node[page_to_nid(page)]--;
-	for (i = 0; i < pages_per_huge_page(h); i++) {
-		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
+	for (i = 0; i < pages_per_huge_page(h);
+	     i++, subpage = mem_map_next(subpage, page, i)) {
+		subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
 				1 << PG_referenced | 1 << PG_dirty |
 				1 << PG_active | 1 << PG_private |
 				1 << PG_writeback);