From 5a49973d7143ebbabd76e1dcd69ee42e349bb7b9 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 14 Jul 2016 12:07:38 -0700 Subject: mm: thp: refix false positive BUG in page_move_anon_rmap() The VM_BUG_ON_PAGE in page_move_anon_rmap() is more trouble than it's worth: the syzkaller fuzzer hit it again. It's still wrong for some THP cases, because linear_page_index() was never intended to apply to addresses before the start of a vma. That's easily fixed with a signed long cast inside linear_page_index(); and Dmitry has tested such a patch, to verify the false positive. But why extend linear_page_index() just for this case? when the avoidance in page_move_anon_rmap() has already grown ugly, and there's no reason for the check at all (nothing else there is using address or index). Remove address arg from page_move_anon_rmap(), remove VM_BUG_ON_PAGE, remove CONFIG_DEBUG_VM PageTransHuge adjustment. And one more thing: should the compound_head(page) be done inside or outside page_move_anon_rmap()? It's usually pushed down to the lowest level nowadays (and mm/memory.c shows no other explicit use of it), so I think it's better done in page_move_anon_rmap() than by caller. Fixes: 0798d3c022dc ("mm: thp: avoid false positive VM_BUG_ON_PAGE in page_move_anon_rmap()") Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1607120444540.12528@eggly.anvils Signed-off-by: Hugh Dickins Reported-by: Dmitry Vyukov Acked-by: Kirill A. Shutemov Cc: Mika Westerberg Cc: Andrea Arcangeli Cc: Rik van Riel Cc: [4.5+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm/hugetlb.c') diff --git a/mm/hugetlb.c b/mm/hugetlb.c index c1f3c0be150a..addfe4accc07 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3383,7 +3383,7 @@ retry_avoidcopy: /* If no-one else is actually using this page, avoid the copy * and just make the page writable */ if (page_mapcount(old_page) == 1 && PageAnon(old_page)) { - page_move_anon_rmap(old_page, vma, address); + page_move_anon_rmap(old_page, vma); set_huge_ptep_writable(vma, address, ptep); return 0; } -- cgit v1.2.3-55-g7522