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 +- mm/memory.c | 3 +-- mm/rmap.c | 9 +++------ 3 files changed, 5 insertions(+), 9 deletions(-) (limited to 'mm') 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; } diff --git a/mm/memory.c b/mm/memory.c index cd1f29e4897e..9e046819e619 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2399,8 +2399,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, * Protected against the rmap code by * the page lock. */ - page_move_anon_rmap(compound_head(old_page), - vma, address); + page_move_anon_rmap(old_page, vma); } unlock_page(old_page); return wp_page_reuse(mm, vma, address, page_table, ptl, diff --git a/mm/rmap.c b/mm/rmap.c index e4b713a6ed7e..701b93fea2a0 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1084,23 +1084,20 @@ EXPORT_SYMBOL_GPL(page_mkclean); * page_move_anon_rmap - move a page to our anon_vma * @page: the page to move to our anon_vma * @vma: the vma the page belongs to - * @address: the user virtual address mapped * * When a page belongs exclusively to one process after a COW event, * that page can be moved into the anon_vma that belongs to just that * process, so the rmap code will not search the parent or sibling * processes. */ -void page_move_anon_rmap(struct page *page, - struct vm_area_struct *vma, unsigned long address) +void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma) { struct anon_vma *anon_vma = vma->anon_vma; + page = compound_head(page); + VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_VMA(!anon_vma, vma); - if (IS_ENABLED(CONFIG_DEBUG_VM) && PageTransHuge(page)) - address &= HPAGE_PMD_MASK; - VM_BUG_ON_PAGE(page->index != linear_page_index(vma, address), page); anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; /* -- cgit v1.2.3