Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753158AbbEKIyd (ORCPT ); Mon, 11 May 2015 04:54:33 -0400 Received: from e28smtp04.in.ibm.com ([122.248.162.4]:49943 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753004AbbEKIyV (ORCPT ); Mon, 11 May 2015 04:54:21 -0400 From: "Aneesh Kumar K.V" To: "Kirill A. Shutemov" Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, kirill.shutemov@linux.intel.com, aarcange@redhat.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3] powerpc/thp: Serialize pmd clear against a linux page table walk. In-Reply-To: <20150511074631.GA10974@node.dhcp.inet.fi> References: <1431325561-21396-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20150511074631.GA10974@node.dhcp.inet.fi> User-Agent: Notmuch/0.19+103~g294bb6d (http://notmuchmail.org) Emacs/24.4.1 (x86_64-pc-linux-gnu) Date: Mon, 11 May 2015 14:24:14 +0530 Message-ID: <87twvj4hqh.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15051108-0013-0000-0000-0000051CA671 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2043 Lines: 50 "Kirill A. Shutemov" writes: > On Mon, May 11, 2015 at 11:56:01AM +0530, Aneesh Kumar K.V wrote: >> Serialize against find_linux_pte_or_hugepte which does lock-less >> lookup in page tables with local interrupts disabled. For huge pages >> it casts pmd_t to pte_t. Since format of pte_t is different from >> pmd_t we want to prevent transit from pmd pointing to page table >> to pmd pointing to huge page (and back) while interrupts are disabled. >> We clear pmd to possibly replace it with page table pointer in >> different code paths. So make sure we wait for the parallel >> find_linux_pte_or_hugepage to finish. >> >> Without this patch, a find_linux_pte_or_hugepte running in parallel to >> __split_huge_zero_page_pmd or do_huge_pmd_wp_page_fallback or zap_huge_pmd >> can run into the above issue. With __split_huge_zero_page_pmd and >> do_huge_pmd_wp_page_fallback we clear the hugepage pte before inserting >> the pmd entry with a regular pgtable address. Such a clear need to >> wait for the parallel find_linux_pte_or_hugepte to finish. >> >> With zap_huge_pmd, we can run into issues, with a hugepage pte >> getting zapped due to a MADV_DONTNEED while other cpu fault it >> in as small pages. >> >> Reported-by: Kirill A. Shutemov >> Signed-off-by: Aneesh Kumar K.V > > Reviewed-by: Kirill A. Shutemov > > CC: stable@ ? Yes, We also need to pick, dac5657067919161eb3273ca787d8ae9814801e7 691e95fd7396905a38d98919e9c150dbc3ea21a3 7d6e7f7ffaba4e013c7a0589140431799bc17985 But that may need me to a backport, because we have dependencies in kvm and a cherry-pick may not work. Will work with Michael Ellerman to find out what needs to be done. -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/