From c0d73261f5c1355a35b8b40e871d31578ce0c044 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 6 Aug 2014 16:05:08 -0700 Subject: [PATCH] mm/memory.c: use entry = ACCESS_ONCE(*pte) in handle_pte_fault() Use ACCESS_ONCE() in handle_pte_fault() when getting the entry or orig_pte upon which all subsequent decisions and pte_same() tests will be made. I have no evidence that its lack is responsible for the mm/filemap.c:202 BUG_ON(page_mapped(page)) in __delete_from_page_cache() found by trinity, and I am not optimistic that it will fix it. But I have found no other explanation, and ACCESS_ONCE() here will surely not hurt. If gcc does re-access the pte before passing it down, then that would be disastrous for correct page fault handling, and certainly could explain the page_mapped() BUGs seen (concurrent fault causing page to be mapped in a second time on top of itself: mapcount 2 for a single pte). Signed-off-by: Hugh Dickins Cc: Sasha Levin Cc: Linus Torvalds Cc: "Kirill A. Shutemov" Cc: Konstantin Khlebnikov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index 8b44f765b645..06ff0720d75a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3181,7 +3181,7 @@ static int handle_pte_fault(struct mm_struct *mm, pte_t entry; spinlock_t *ptl; - entry = *pte; + entry = ACCESS_ONCE(*pte); if (!pte_present(entry)) { if (pte_none(entry)) { if (vma->vm_ops) { -- 2.25.1