From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Hugh Dickins , Sasha Levin , Linus Torvalds , "Kirill A. Shutemov" , Konstantin Khlebnikov , Andrew Morton , Mel Gorman Subject: [PATCH 3.14 65/77] mm/memory.c: use entry = ACCESS_ONCE(*pte) in handle_pte_fault() Date: Tue, 27 Jan 2015 17:27:43 -0800 Message-Id: <20150128012747.919048398@linuxfoundation.org> In-Reply-To: <20150128012745.971137091@linuxfoundation.org> References: <20150128012745.971137091@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Hugh Dickins commit c0d73261f5c1355a35b8b40e871d31578ce0c044 upstream. 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 Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/memory.c +++ b/mm/memory.c @@ -3646,7 +3646,7 @@ static int handle_pte_fault(struct mm_st pte_t entry; spinlock_t *ptl; - entry = *pte; + entry = ACCESS_ONCE(*pte); if (!pte_present(entry)) { if (pte_none(entry)) { if (vma->vm_ops) {