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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 69C01C433DF 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 246A3206F1 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 246A3206F1 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) Received: by kanga.kvack.org (Postfix, from userid 40) id B4CB880010; Thu, 28 May 2020 01:20:49 -0400 (EDT) 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-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-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; _