From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754055AbcEWPIa (ORCPT ); Mon, 23 May 2016 11:08:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48656 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752409AbcEWPI3 (ORCPT ); Mon, 23 May 2016 11:08:29 -0400 Date: Mon, 23 May 2016 17:08:26 +0200 From: Andrea Arcangeli To: Mika Westerberg Cc: "Kirill A. Shutemov" , linux-kernel@vger.kernel.org Subject: Re: v4.6 kernel BUG at mm/rmap.c:1101! Message-ID: <20160523150826.GA20829@redhat.com> References: <20160523140638.GA1738@lahna.fi.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160523140638.GA1738@lahna.fi.intel.com> User-Agent: Mutt/1.6.1 (2016-04-27) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 23 May 2016 15:08:28 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 23, 2016 at 05:06:38PM +0300, Mika Westerberg wrote: > Hi, > > After upgrading kernel of my desktop system from v4.6-rc7 to v4.6, I've > started seeing following: > > [176611.093747] page:ffffea0000360000 count:1 mapcount:0 mapping:ffff880034d2e0a1 index:0x1f9b06600 compound_mapcount: 0 > [176611.093751] flags: 0x3fff8000044079(locked|uptodate|dirty|lru|active|head|swapbacked) > [176611.093752] page dumped because: VM_BUG_ON_PAGE(page->index != linear_page_index(vma, address)) > [176611.093753] page->mem_cgroup:ffff88049e81b800 > [176611.093765] ------------[ cut here ]------------ This is a splitted pmd tail that is triggering a COW, but it's still a compound page because the physical split didn't happen yet. So like Kirill correctly pointed out, in such case we've to do compound_head because the page->mapping that has to be refiled to the local anon_vma is in the head. It's just a false positive VM_BUG_ON, the code itself is correct. Production kernels should be built with CONFIG_DEBUG_VM=n so this is not going to affect them and there's no bug for the production builds. Can you test this to shut off the false positive? >>From 4db87e3e44837a0b038e58eaa3fea29db84723ec Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Mon, 23 May 2016 17:03:57 +0200 Subject: [PATCH 1/1] mm: thp: avoid false positive VM_BUG_ON_PAGE in page_move_anon_rmap() If the page_move_anon_rmap() is refiling a pmd-splitted THP mapped in a tail page from a pte, the "address" must be THP aligned in order for the page->index bugcheck to pass in the CONFIG_DEBUG_VM=y builds. Signed-off-by: Andrea Arcangeli --- mm/rmap.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/rmap.c b/mm/rmap.c index 8a83993..e2e47ba9 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1098,7 +1098,10 @@ void page_move_anon_rmap(struct page *page, VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_VMA(!anon_vma, vma); - VM_BUG_ON_PAGE(page->index != linear_page_index(vma, address), page); + VM_BUG_ON_PAGE(page->index != + linear_page_index(vma, PageTransHuge(page) ? + address & HPAGE_PMD_MASK : + address), page); anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; /*