From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932355AbcEXIOR (ORCPT ); Tue, 24 May 2016 04:14:17 -0400 Received: from mga02.intel.com ([134.134.136.20]:43112 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754671AbcEXIM1 (ORCPT ); Tue, 24 May 2016 04:12:27 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,359,1459839600"; d="scan'208";a="109388372" Date: Tue, 24 May 2016 11:12:23 +0300 From: Mika Westerberg To: Andrea Arcangeli Cc: "Kirill A. Shutemov" , linux-kernel@vger.kernel.org Subject: Re: v4.6 kernel BUG at mm/rmap.c:1101! Message-ID: <20160524081223.GE1712@lahna.fi.intel.com> References: <20160523140638.GA1738@lahna.fi.intel.com> <20160523150826.GA20829@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160523150826.GA20829@redhat.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 23, 2016 at 05:08:26PM +0200, Andrea Arcangeli wrote: > 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. OK, thanks for the explanation. > 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. Hmm, the kernel shipped with Fedora 23 has that enabled: lahna % grep CONFIG_DEBUG_VM /boot/config-4.4.9-300.fc23.x86_64 CONFIG_DEBUG_VM=y # CONFIG_DEBUG_VM_VMACACHE is not set # CONFIG_DEBUG_VM_RB is not set > Can you test this to shut off the false positive? I'm testing with Kirill's patch (because he sent it first ;-)) and let you know what happens. Thanks!