From patchwork Thu May 28 05:20:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 11574675 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id DDED61392 for ; Thu, 28 May 2020 05:20:50 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AB14C206F1 for ; Thu, 28 May 2020 05:20:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="RolBtyCN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB14C206F1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BEB6D800B8; Thu, 28 May 2020 01:20:49 -0400 (EDT) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id B4CB880010; Thu, 28 May 2020 01:20:49 -0400 (EDT) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A3CF1800B8; Thu, 28 May 2020 01:20:49 -0400 (EDT) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0120.hostedemail.com [216.40.44.120]) by kanga.kvack.org (Postfix) with ESMTP id 8CC2C80010 for ; Thu, 28 May 2020 01:20:49 -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 504292480 for ; Thu, 28 May 2020 05:20:49 +0000 (UTC) X-FDA: 76864978218.12.print09_243676817565a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 316CB18056270 for ; Thu, 28 May 2020 05:20:49 +0000 (UTC) X-Spam-Summary: 10,1,0,e202569066604494,d41d8cd98f00b204,akpm@linux-foundation.org,,RULES_HIT:41:69:355:379:800:960:966:967:968:973:988:989:1260:1263:1345:1359:1381:1431:1437:1535:1543:1711:1730:1747:1777:1792:2196:2198:2199:2200:2393:2525:2559:2565:2682:2685:2731:2859:2902:2933:2937:2939:2942:2945:2947:2951:2954:3022:3138:3139:3140:3141:3142:3354:3503:3504:3505:3866:3867:3868:3870:3871:3872:3934:3936:3938:3941:3944:3947:3950:3953:3956:3959:4250:4321:4385:4605:5007:6119:6261:6653:7576:7903:7904:8599:8784:8957:9025:9163:9207:9545:9592:10004:10913:11026:11232:11473:11658:11914:12043:12048:12114:12295:12296:12297:12438:12517:12519:12555:12679:12700:12737:12740:12783:12895:12986:13161:13229:13870:14093:14096:14181:14721:14849:14915:21080:21220:21365:21433:21451:21627:21740:21749:21811:21889:21939:21990:30012:30029:30054:30056:30070,0,RBL:198.145.29.99:@linux-foundation.org:.lbl8.mailshell.net-64.100.201.201 62.2.0.100,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0, MSF:not X-HE-Tag: print09_243676817565a X-Filterd-Recvd-Size: 5094 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Thu, 28 May 2020 05:20:48 +0000 (UTC) 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 B11EC214D8; Thu, 28 May 2020 05:20:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590643248; bh=8tCTkuTf5baAgcrzO+4dGrd4I82G8UI7OYXJcM8GIWE=; h=Date:From:To:Subject:In-Reply-To:From; b=RolBtyCNalA5BEpnBE1qMs42A0JC7nvB/R7djh0EiLlS5AK6CWdzgx5aLYvt5HKis WT6mppgWjtJKOKtAzJ6NbukIgfkPh+pQnwy7dqSJV2yZBOEHq71nrY5LrM3YTjXRuJ mSXZ1nXMx0/T+hGrYSyU0ySzR1TOd+cflKw5Yjs0= Date: Wed, 27 May 2020 22:20:47 -0700 From: Andrew Morton To: akpm@linux-foundation.org, hughd@google.com, khlebnikov@yandex-team.ru, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, rientjes@google.com, stable@vger.kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 3/5] mm: remove VM_BUG_ON(PageSlab()) from page_mapcount() Message-ID: <20200528052047.tDxIOLXzt%akpm@linux-foundation.org> In-Reply-To: <20200527222015.62ba8592af63dae12ab58ffe@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Rspamd-Queue-Id: 316CB18056270 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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: From: Konstantin Khlebnikov Subject: mm: remove VM_BUG_ON(PageSlab()) from page_mapcount() 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). [akpm@linux-foundation.org: comment tweaks, per Hugh] 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) Fixes: 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()") Signed-off-by: Konstantin Khlebnikov Acked-by: Hugh Dickins Acked-by: Kirill A. Shutemov Acked-by: Vlastimil Babka Cc: David Rientjes Cc: Signed-off-by: Andrew Morton --- include/linux/mm.h | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) --- a/include/linux/mm.h~mm-remove-vm_bug_onpageslab-from-page_mapcount +++ a/include/linux/mm.h @@ -782,6 +782,11 @@ static inline void *kvcalloc(size_t n, s extern void kvfree(const void *addr); +/* + * Mapcount of compound page as a whole, does not include mapped sub-pages. + * + * Must be called only for compound pages or any their tail sub-pages. + */ static inline int compound_mapcount(struct page *page) { VM_BUG_ON_PAGE(!PageCompound(page), page); @@ -801,10 +806,16 @@ static inline void page_mapcount_reset(s int __page_mapcount(struct page *page); +/* + * Mapcount of 0-order page; when compound sub-page, includes + * compound_mapcount(). + * + * Result is undefined for pages which cannot be mapped into userspace. + * For example SLAB or special types of pages. See function page_has_type(). + * They use this place in struct page differently. + */ static inline int page_mapcount(struct page *page) { - VM_BUG_ON_PAGE(PageSlab(page), page); - if (unlikely(PageCompound(page))) return __page_mapcount(page); return atomic_read(&page->_mapcount) + 1;