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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 BD883C433DF for ; Mon, 1 Jun 2020 18:59:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9565520679 for ; Mon, 1 Jun 2020 18:59:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591037970; bh=YYkXeT0qG5PVYrGeJGIoToGBNE1ZhrA2NGX8vI6bL6I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Nv62wgcXidH1mxcaF/qaZnYDxGhRtz0aA1HGO6TFkrLEC8Urk8z52DDNOES2yJMJu J8TmqMzYRmuT7YSFaPnYQYBf/6VZqO6bJIajCRrr6RCkxeBIpjgN0A+41NunWJ5xsh O2aJpMu+AYVa80WCHhm41baxPLB93ILh7C5AhecU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728884AbgFAR5Z (ORCPT ); Mon, 1 Jun 2020 13:57:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:38574 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728903AbgFAR5Y (ORCPT ); Mon, 1 Jun 2020 13:57:24 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 E5B662073B; Mon, 1 Jun 2020 17:57:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591034243; bh=YYkXeT0qG5PVYrGeJGIoToGBNE1ZhrA2NGX8vI6bL6I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pWmGAjDB9UV7ybE3yoLIsFAcyAjhP8Z7jUUpxfu+EaRg4zwqvUrJuQZCO9HSKx2Hj 1PYdRWiMJKmGgdGR/2W0R30BYccd2i8TypnJXZ4JxlpJewuVZgzdHRvOsOXOwhvb98 dDRPtlMy+p3R8fg0fqiUFWOBNKW9VOcxK6M9BKmY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Konstantin Khlebnikov , Andrew Morton , Hugh Dickins , "Kirill A. Shutemov" , Vlastimil Babka , David Rientjes , Linus Torvalds Subject: [PATCH 4.4 39/48] mm: remove VM_BUG_ON(PageSlab()) from page_mapcount() Date: Mon, 1 Jun 2020 19:53:49 +0200 Message-Id: <20200601174003.327414437@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200601173952.175939894@linuxfoundation.org> References: <20200601173952.175939894@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Konstantin Khlebnikov commit 6988f31d558aa8c744464a7f6d91d34ada48ad12 upstream. Replace superfluous VM_BUG_ON() with comment about correct usage. Technically reverts commit 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()"), but context lines 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 The 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). [akpm@linux-foundation.org: comment tweaks, per Hugh] Fixes: 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()") Signed-off-by: Konstantin Khlebnikov Signed-off-by: Andrew Morton Acked-by: Hugh Dickins Acked-by: Kirill A. Shutemov Acked-by: Vlastimil Babka Cc: David Rientjes Cc: Link: http://lkml.kernel.org/r/159032779896.957378.7852761411265662220.stgit@buzz Link: https://lore.kernel.org/lkml/557710E1.6060103@suse.cz/ Link: https://lore.kernel.org/linux-mm/158937872515.474360.5066096871639561424.stgit@buzz/T/ (v1) Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- include/linux/mm.h | 1 - 1 file changed, 1 deletion(-) --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -446,7 +446,6 @@ static inline void page_mapcount_reset(s static inline int page_mapcount(struct page *page) { - VM_BUG_ON_PAGE(PageSlab(page), page); return atomic_read(&page->_mapcount) + 1; }