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 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 E5FFAC433DF for ; Mon, 25 May 2020 00:49:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC2B12071C for ; Mon, 25 May 2020 00:49:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590367750; bh=uCR+1vMGNuwkpY3ylH3icm/d3NygVTO7vRWcCaC3fUo=; h=Date:From:To:Subject:In-Reply-To:List-ID:From; b=O5nJXUSVwhvaI9swXuBCuSpHZWd9f3zsZV5hvZGK6UTKIdpGb1luVrFgbynXTciyJ 9VkOHWt85kLI/b/4oh99CMIdeREDYCds3Moocb3Oe0dH+2pMGnsn0SglUMlEkn4Dld BakWK5k+htRK6bNtochFXNZpR6nnwxHM2BXUGCtc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388340AbgEYAtK (ORCPT ); Sun, 24 May 2020 20:49:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:46612 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388014AbgEYAtK (ORCPT ); Sun, 24 May 2020 20:49:10 -0400 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 DB9D920674; Mon, 25 May 2020 00:49:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590367749; bh=uCR+1vMGNuwkpY3ylH3icm/d3NygVTO7vRWcCaC3fUo=; h=Date:From:To:Subject:In-Reply-To:From; b=VUASvHqD43OL9569wqZ41zf/uJifX5WaE4Q3WPPUr3QlWMR0jZ+6Bq1lIFN6GgI33 IYwitEkpi8inQBBHW2kPgPNV84A/d4Rks/LtBPBP1nmGeml5QgCzrAFqu8qWf1KNyX LEgBSXSGIjF0sTGhlygZ4U3xcQumY7mSfrx/b/7I= Date: Sun, 24 May 2020 17:49:08 -0700 From: Andrew Morton To: hughd@google.com, khlebnikov@yandex-team.ru, kirill.shutemov@linux.intel.com, mm-commits@vger.kernel.org, rientjes@google.com, stable@vger.kernel.org, vbabka@suse.cz Subject: + mm-remove-vm_bug_onpageslab-from-page_mapcount.patch added to -mm tree Message-ID: <20200525004908.ptY_Df6aP%akpm@linux-foundation.org> In-Reply-To: <20200522222217.ee14ad7eda7aab1e6697da6c@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: mm: remove VM_BUG_ON(PageSlab()) from page_mapcount() has been added to the -mm tree. Its filename is mm-remove-vm_bug_onpageslab-from-page_mapcount.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-remove-vm_bug_onpageslab-from-page_mapcount.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-remove-vm_bug_onpageslab-from-page_mapcount.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ 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). 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 Cc: Vlastimil Babka Cc: David Rientjes Cc: "Kirill A. Shutemov" Cc: Signed-off-by: Andrew Morton --- include/linux/mm.h | 14 ++++++++++++-- 1 file changed, 12 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, not includes 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 +806,15 @@ static inline void page_mapcount_reset(s int __page_mapcount(struct page *page); +/* + * Mapcount of 0-order page, for 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; _ Patches currently in -mm which might be from khlebnikov@yandex-team.ru are mm-compaction-avoid-vm_bug_onpageslab-in-page_mapcount.patch mm-remove-vm_bug_onpageslab-from-page_mapcount.patch kernel-watchdog-flush-all-printk-nmi-buffers-when-hardlockup-detected.patch doc-cgroup-update-note-about-conditions-when-oom-killer-is-invoked.patch