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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 4B7D0C433E2 for ; Mon, 1 Jun 2020 18:51:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 29A8920679 for ; Mon, 1 Jun 2020 18:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591037497; bh=HfDsW7E7FnbB8ARdUvhq0rfqvewORS1KytEwONRTS0c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=XmHpBkEQttEzn7H9zxDS8vVV+AMnMf93bEUdo/BmUqQAdPv9WZ6OLyz3ojE5RwckD pF+TpzC35W0kJEtqhJLtxeCdOF2v33slpEocVrUW9Ef2nOXyuOTU9DrdPEPyCYn74t mSRflFhc0ZBBqSFLD6sSO3J1Of7pj1DcCVHDKf1M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730265AbgFASEy (ORCPT ); Mon, 1 Jun 2020 14:04:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:49790 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730261AbgFASEx (ORCPT ); Mon, 1 Jun 2020 14:04:53 -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 5B07F206E2; Mon, 1 Jun 2020 18:04:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591034691; bh=HfDsW7E7FnbB8ARdUvhq0rfqvewORS1KytEwONRTS0c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=067COvTN8iDmDJ0VssX8yX1O1cmihJ0swps9A5Oec+lcDqMlyf8DFt4x82JHB8MAf MrkATZqyjqQ1v1jFqAEHxYs/wVTuG3hI7jK4l62jGeDxLyGtsW6IHtQbwT8ndQA95H azyd07XUMyPa3qrF3Zw2JMDnUALZE4eC/d6aBJvM= 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 , Sasha Levin Subject: [PATCH 4.19 65/95] mm: remove VM_BUG_ON(PageSlab()) from page_mapcount() Date: Mon, 1 Jun 2020 19:54:05 +0200 Message-Id: <20200601174031.285173461@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200601174020.759151073@linuxfoundation.org> References: <20200601174020.759151073@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 [ Upstream commit 6988f31d558aa8c744464a7f6d91d34ada48ad12 ] 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: Sasha Levin --- include/linux/mm.h | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 45f10f5896b7..b1092046ebef 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -602,6 +602,11 @@ static inline void *kvcalloc(size_t n, size_t size, gfp_t flags) 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); @@ -621,10 +626,16 @@ static inline void page_mapcount_reset(struct page *page) 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; -- 2.25.1