From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A405C433E0 for ; Wed, 13 May 2020 18:33:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D79FF206F5 for ; Wed, 13 May 2020 18:33:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589394781; bh=Qfxp4RkKifYwn+DnBDj1Wn+LE1G0Gl079k/dFlALe0M=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=0noBrjQFW18EQclgz0E0JaLrkKm8V8zEE1GfbG2tDf97NxDJgoEfwRMz4osBBPkXf ge1yl4zG3g3iDp1ti+4xkSmtWFR0T+KehSMATk5wmyW/1lqlnnXFbuDKbbVzxTWdKf Yfs+VtIfuHTlluCA2kA9/jDJ109YPiZ48RJ9YhJ8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390190AbgEMSdA (ORCPT ); Wed, 13 May 2020 14:33:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:48904 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390079AbgEMSc7 (ORCPT ); Wed, 13 May 2020 14:32:59 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4540020671; Wed, 13 May 2020 18:32:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589394778; bh=Qfxp4RkKifYwn+DnBDj1Wn+LE1G0Gl079k/dFlALe0M=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=s4ru3/GKMct8lOhciaqKnieA8fhnb4v3LdxyKiCkzRLYN6P/1jGU+5NcS9gkBylKQ iRPU/O2e/goa+dLm6nHmT/1jtW0qGkleo598rUPDaccnevF5fXVzwP6SbgCuiAu9Rb e9Nx72ixY6btNYYs9R4u0xsNXkTTNGaPrmPbp3UQ= Date: Wed, 13 May 2020 11:32:56 -0700 From: Andrew Morton To: Konstantin Khlebnikov Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , Vlastimil Babka , David Rientjes , Mel Gorman Subject: Re: [PATCH] mm/compaction: avoid VM_BUG_ON(PageSlab()) in page_mapcount() Message-Id: <20200513113256.44ac9ce4c51a7ec1a5c5ba40@linux-foundation.org> In-Reply-To: <158937872515.474360.5066096871639561424.stgit@buzz> References: <158937872515.474360.5066096871639561424.stgit@buzz> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 May 2020 17:05:25 +0300 Konstantin Khlebnikov wrote: > Function isolate_migratepages_block() runs some checks out of lru_lock > when choose pages for migration. After checking PageLRU() it checks extra > page references by comparing page_count() and page_mapcount(). Between > these two checks page could be removed from lru, freed and taken by slab. > > As a result this race triggers VM_BUG_ON(PageSlab()) in page_mapcount(). > Race window is tiny. For certain workload this happens around once a year. > > > page:ffffea0105ca9380 count:1 mapcount:0 mapping:ffff88ff7712c180 index:0x0 compound_mapcount: 0 > flags: 0x500000000008100(slab|head) > raw: 0500000000008100 dead000000000100 dead000000000200 ffff88ff7712c180 > raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000 > page dumped because: VM_BUG_ON_PAGE(PageSlab(page)) > ------------[ cut here ]------------ > kernel BUG at ./include/linux/mm.h:628! > invalid opcode: 0000 [#1] SMP NOPTI > CPU: 77 PID: 504 Comm: kcompactd1 Tainted: G W 4.19.109-27 #1 > Hardware name: Yandex T175-N41-Y3N/MY81-EX0-Y3N, BIOS R05 06/20/2019 > RIP: 0010:isolate_migratepages_block+0x986/0x9b0 > > > To fix just opencode page_mapcount() in racy check for 0-order case and > recheck carefully under lru_lock when page cannot escape from lru. > > Also add checking extra references for file pages and swap cache. It sounds like a cc:stable is appropriate? > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -935,12 +935,16 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > } > > /* > - * Migration will fail if an anonymous page is pinned in memory, > + * Migration will fail if an page is pinned in memory, > * so avoid taking lru_lock and isolating it unnecessarily in an > - * admittedly racy check. > + * admittedly racy check simplest case for 0-order pages. > + * > + * Open code page_mapcount() to avoid VM_BUG_ON(PageSlab(page)). > + * Page could have extra reference from mapping or swap cache. > */ > - if (!page_mapping(page) && > - page_count(page) > page_mapcount(page)) > + if (!PageCompound(page) && > + page_count(page) > atomic_read(&page->_mapcount) + 1 + > + (!PageAnon(page) || PageSwapCache(page))) > goto isolate_fail; > > /* > @@ -975,6 +979,11 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > low_pfn += compound_nr(page) - 1; > goto isolate_fail; > } > + > + /* Recheck page extra references under lock */ > + if (page_count(page) > page_mapcount(page) + > + (!PageAnon(page) || PageSwapCache(page))) > + goto isolate_fail; > } > > lruvec = mem_cgroup_page_lruvec(page, pgdat);