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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 E97C6CA90AF for ; Wed, 13 May 2020 14:05:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0571F204EF for ; Wed, 13 May 2020 14:05:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="uKlmcMdr" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0571F204EF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=yandex-team.ru Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 01C15900132; Wed, 13 May 2020 10:05:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F0F5A9000F3; Wed, 13 May 2020 10:05:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E2444900132; Wed, 13 May 2020 10:05:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0076.hostedemail.com [216.40.44.76]) by kanga.kvack.org (Postfix) with ESMTP id C6F279000F3 for ; Wed, 13 May 2020 10:05:30 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 829A93CE9 for ; Wed, 13 May 2020 14:05:30 +0000 (UTC) X-FDA: 76811868420.12.body64_6a22d26431a63 X-HE-Tag: body64_6a22d26431a63 X-Filterd-Recvd-Size: 4930 Received: from forwardcorp1p.mail.yandex.net (forwardcorp1p.mail.yandex.net [77.88.29.217]) by imf11.hostedemail.com (Postfix) with ESMTP for ; Wed, 13 May 2020 14:05:29 +0000 (UTC) Received: from mxbackcorp1o.mail.yandex.net (mxbackcorp1o.mail.yandex.net [IPv6:2a02:6b8:0:1a2d::301]) by forwardcorp1p.mail.yandex.net (Yandex) with ESMTP id 8DD192E1574; Wed, 13 May 2020 17:05:26 +0300 (MSK) Received: from vla5-58875c36c028.qloud-c.yandex.net (vla5-58875c36c028.qloud-c.yandex.net [2a02:6b8:c18:340b:0:640:5887:5c36]) by mxbackcorp1o.mail.yandex.net (mxbackcorp/Yandex) with ESMTP id lDNVHsY2qe-5PpWqbZP; Wed, 13 May 2020 17:05:26 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1589378726; bh=YcgwTTe1UbCJlZpmvqFenHMREDNQ+pyRS2BjsAD24bI=; h=Message-ID:Date:To:From:Subject; b=uKlmcMdrccVnLpz/QJl9j1Ey7nEKddWJIRk1JUu4m/QIveLUfUYAWEKqDIYGbb800 mBsTcVVjP+JjseIGcjGGTkrpT3E3d4T0ecgMmvFQfM3RphHi1iibKy1oumAEn23d58 aQV6jUfXskRAFLYwhM72Uw8k7ErDA1NYw3Z1JXeg= Authentication-Results: mxbackcorp1o.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Received: from dynamic-vpn.dhcp.yndx.net (dynamic-vpn.dhcp.yndx.net [2a02:6b8:b080:8207::1:2]) by vla5-58875c36c028.qloud-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id MK10jIJZJE-5PXuZchK; Wed, 13 May 2020 17:05:25 +0300 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client certificate not present) Subject: [PATCH] mm/compaction: avoid VM_BUG_ON(PageSlab()) in page_mapcount() From: Konstantin Khlebnikov To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton Date: Wed, 13 May 2020 17:05:25 +0300 Message-ID: <158937872515.474360.5066096871639561424.stgit@buzz> User-Agent: StGit/0.22-39-gd257 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. Signed-off-by: Konstantin Khlebnikov Fixes: 119d6d59dcc0 ("mm, compaction: avoid isolating pinned pages") Fixes: 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()") --- mm/compaction.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 46f0fcc93081..91bb87fd9420 100644 --- 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);