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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 D60B7C433E0 for ; Wed, 13 May 2020 19:28:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6F003206CC for ; Wed, 13 May 2020 19:28:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="EFTQt8g0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F003206CC 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 28A0E80030; Wed, 13 May 2020 15:28:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 23B3A8000B; Wed, 13 May 2020 15:28:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1508D80030; Wed, 13 May 2020 15:28:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0183.hostedemail.com [216.40.44.183]) by kanga.kvack.org (Postfix) with ESMTP id EE1318000B for ; Wed, 13 May 2020 15:28:06 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 9A085181AEF09 for ; Wed, 13 May 2020 19:28:06 +0000 (UTC) X-FDA: 76812681372.06.teeth26_c6c48d033d28 X-HE-Tag: teeth26_c6c48d033d28 X-Filterd-Recvd-Size: 5586 Received: from forwardcorp1j.mail.yandex.net (forwardcorp1j.mail.yandex.net [5.45.199.163]) by imf35.hostedemail.com (Postfix) with ESMTP for ; Wed, 13 May 2020 19:28:05 +0000 (UTC) Received: from mxbackcorp1o.mail.yandex.net (mxbackcorp1o.mail.yandex.net [IPv6:2a02:6b8:0:1a2d::301]) by forwardcorp1j.mail.yandex.net (Yandex) with ESMTP id 077462E152B; Wed, 13 May 2020 22:28:03 +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 i4BcqtDHk9-S1pOG51g; Wed, 13 May 2020 22:28:02 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1589398082; bh=cJi+YKhtTW0lmQ8DVzDb4gU8JozSoYxkOvuTMg1aLOM=; h=In-Reply-To:Message-ID:From:Date:References:To:Subject:Cc; b=EFTQt8g02sOjiShkvplXhQAnbLHvu+FwRSFw3N7JvhAHJ8htGGT6jzHQ58eiGRDIy /a6FN69X1eol0F5aD2k2cebN+FYSlUc7fXrWvlcK5WndT2X7h/hTP3TYbAxExVPCME 1fMsx5UwJ76J3whY246zHZ78CI8o5m7PCBdzhdec= 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:b081:407::1:3]) by vla5-58875c36c028.qloud-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id XzeIGzjjyK-S1Xu46ha; Wed, 13 May 2020 22:28:01 +0300 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client certificate not present) Subject: Re: [PATCH] mm/compaction: avoid VM_BUG_ON(PageSlab()) in page_mapcount() To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , Vlastimil Babka , David Rientjes , Mel Gorman References: <158937872515.474360.5066096871639561424.stgit@buzz> <20200513113256.44ac9ce4c51a7ec1a5c5ba40@linux-foundation.org> From: Konstantin Khlebnikov Message-ID: <9420f90c-e423-475c-4b79-8287b76149d9@yandex-team.ru> Date: Wed, 13 May 2020 22:28:00 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200513113256.44ac9ce4c51a7ec1a5c5ba40@linux-foundation.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-CA 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: On 13/05/2020 21.32, Andrew Morton wrote: > 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? Yep, but probably I'm missing something. It seems bug is there for a long time and nobody seen it. Am I the only one using COONFIG_DEBUG_VM=y everywhere? =) > >> --- 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);