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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29E11C4332F for ; Wed, 16 Nov 2022 15:47:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233195AbiKPPrW (ORCPT ); Wed, 16 Nov 2022 10:47:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58588 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233247AbiKPPrT (ORCPT ); Wed, 16 Nov 2022 10:47:19 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DEFC342F75 for ; Wed, 16 Nov 2022 07:47:16 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5960B150C; Wed, 16 Nov 2022 07:47:18 -0800 (PST) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.35.169]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 079933F587; Wed, 16 Nov 2022 07:47:06 -0800 (PST) Date: Wed, 16 Nov 2022 15:46:59 +0000 From: Mark Rutland To: David Hildenbrand Cc: Liu Shixin , Catalin Marinas , Will Deacon , Denys Vlasenko , Kefeng Wang , Anshuman Khandual , David Hildenbrand , Rafael Aquini , Pasha Tatashin , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] arm64/mm: fix incorrect file_map_count for invalid pmd/pud Message-ID: References: <20221116083811.464678-1-liushixin2@huawei.com> <20221116083811.464678-3-liushixin2@huawei.com> <73189e81-08c2-bb18-dd4a-f717996ea819@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <73189e81-08c2-bb18-dd4a-f717996ea819@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 16, 2022 at 10:08:27AM +0100, David Hildenbrand wrote: > On 16.11.22 09:38, Liu Shixin wrote: > > The page table check trigger BUG_ON() unexpectedly when split hugepage: > > > > ------------[ cut here ]------------ > > kernel BUG at mm/page_table_check.c:119! > > Internal error: Oops - BUG: 00000000f2000800 [#1] SMP > > Dumping ftrace buffer: > > (ftrace buffer empty) > > Modules linked in: > > CPU: 7 PID: 210 Comm: transhuge-stres Not tainted 6.1.0-rc3+ #748 > > Hardware name: linux,dummy-virt (DT) > > pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) > > pc : page_table_check_set.isra.0+0x398/0x468 > > lr : page_table_check_set.isra.0+0x1c0/0x468 > > [...] > > Call trace: > > page_table_check_set.isra.0+0x398/0x468 > > __page_table_check_pte_set+0x160/0x1c0 > > __split_huge_pmd_locked+0x900/0x1648 > > __split_huge_pmd+0x28c/0x3b8 > > unmap_page_range+0x428/0x858 > > unmap_single_vma+0xf4/0x1c8 > > zap_page_range+0x2b0/0x410 > > madvise_vma_behavior+0xc44/0xe78 > > do_madvise+0x280/0x698 > > __arm64_sys_madvise+0x90/0xe8 > > invoke_syscall.constprop.0+0xdc/0x1d8 > > do_el0_svc+0xf4/0x3f8 > > el0_svc+0x58/0x120 > > el0t_64_sync_handler+0xb8/0xc0 > > el0t_64_sync+0x19c/0x1a0 > > [...] > > > > On arm64, pmd_present() will return true even if the pmd is invalid. > > I assume that's because of the pmd_present_invalid() check. > > ... I wonder why that behavior was chosen. Sounds error-prone to me. That seems to be down to commit: b65399f6111b03df ("arm64/mm: Change THP helpers to comply with generic MM semantics") ... apparently because Andrea Arcangelli said this was necessary in: https://lore.kernel.org/lkml/20181017020930.GN30832@redhat.com/ ... but that does see to contradict what's said in: Documentation/mm/arch_pgtable_helpers.rst ... which just says: pmd_present Tests a valid mapped PMD ... and it's not clear to me why this *only* applies to the PMD level. Anshuman? Thanks, Mark.