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=-3.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 2D35CC433E1 for ; Mon, 25 May 2020 04:44:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0E7DC2071A for ; Mon, 25 May 2020 04:44:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="09rI4km/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388211AbgEYEon (ORCPT ); Mon, 25 May 2020 00:44:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725948AbgEYEom (ORCPT ); Mon, 25 May 2020 00:44:42 -0400 Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3083FC061A0E for ; Sun, 24 May 2020 21:44:41 -0700 (PDT) Received: by mail-lj1-x244.google.com with SMTP id c11so17146586ljn.2 for ; Sun, 24 May 2020 21:44:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=M6jtbeZwsvOZY+pgkpyuXhsDWBq5iskp0QmwZ/y8vek=; b=09rI4km/OQky2Hmq6IxNeoiKo6N0pt5n/f/PKfR13+ShQ85KtKze6oAlKD20TZz3uG hK5itjdR+DGUWy/ck/g9o7zoYj1sAuEP/l/vuQ8JCscuFmDGnBGFvXFadRkAawaWY0sJ 0GRmmleoZL098cmRsHe9hqsJZPjZedVJdbOuQg+rsr1tUNBhltwHGHylxhgppz2OZR+/ zMrJ5vxrxqGrV0sUX9B94ozLmcIf/Dc80Xt4z0bGSMn8sMtdhstvP4oVMijucS84XTKf mIbFWn7F5XzMuJCCV2ik6sf3HKVDp8MW9hA8nR88LHJLbytPYmBBk2Qxvpsxuh0TQhyl R1pQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=M6jtbeZwsvOZY+pgkpyuXhsDWBq5iskp0QmwZ/y8vek=; b=qxd6PvqrSwBhR+21UXK6sjd1fRN+50hpQConqJ6uIx0BKul/WqSP3qCdDRf0qAv0DY 2PpkHhkPDomrVXc+fW+X1BjfOQ9LRdBeOoWgLjwvAi9WMtqK91gZwpCD+Oy0lkq2UGzz XGiAm7uxOJVeP04JtzknL1HuiAJo3ovCi4HDzdG+oRU8PRxeizV4o+rI2TJwsJjYaoUd 0GN8aD3+7wrODdf3QZHQzmkOAf9KfsK1vsErtbpNg84ABCW+3TtxUMxXrMWC3dQrv4ML YF8MLvrEmGFN1ZM1fT11uVkFKRzqyrI3+8DKRN0UJN3ovJQ7/9r2iRmM/auFKPX6FZZI vwtQ== X-Gm-Message-State: AOAM531k7bZ8/gwS9ewtPuTBe+3/ymJX2zFN6wkfXMDsxWFYtQ5rqtgY f1izdlGI4dlNsbikDNWkzsTRZw== X-Google-Smtp-Source: ABdhPJw50Z60Kd3jiZW8ttE5tCSoWdYL5faK1qntPLqAT1rgXHSslGhNq6uCYyWrH2iB5zTGkI3frg== X-Received: by 2002:a2e:8997:: with SMTP id c23mr13748654lji.22.1590381879513; Sun, 24 May 2020 21:44:39 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id h2sm4733454ljb.45.2020.05.24.21.44.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 24 May 2020 21:44:38 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id 72CDA1012E6; Mon, 25 May 2020 07:44:39 +0300 (+03) Date: Mon, 25 May 2020 07:44:39 +0300 From: "Kirill A. Shutemov" To: Konstantin Khlebnikov Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Hugh Dickins , Vlastimil Babka , David Rientjes , "Kirill A. Shutemov" Subject: Re: [PATCH v2] mm: remove VM_BUG_ON(PageSlab()) from page_mapcount() Message-ID: <20200525044439.f433y6enrpehdmid@box> References: <159032779896.957378.7852761411265662220.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <159032779896.957378.7852761411265662220.stgit@buzz> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 24, 2020 at 04:43:18PM +0300, Konstantin Khlebnikov wrote: > Replace superfluous VM_BUG_ON() with comment about correct usage. > > Technically reverts commit 1d148e218a0d0566b1c06f2f45f1436d53b049b2 > ("mm: add VM_BUG_ON_PAGE() to page_mapcount()"), but context have changed. > > 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 > > > Code in isolate_migratepages_block() was added in commit 119d6d59dcc0 > ("mm, compaction: avoid isolating pinned pages") before adding VM_BUG_ON > into page_mapcount(). > > This race has been predicted in 2015 by Vlastimil Babka (see link below). > > Signed-off-by: Konstantin Khlebnikov > Fixes: 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()") > Link: https://lore.kernel.org/lkml/557710E1.6060103@suse.cz/ > Link: https://lore.kernel.org/linux-mm/158937872515.474360.5066096871639561424.stgit@buzz/T/ (v1) Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov