Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750774AbbEKHrI (ORCPT ); Mon, 11 May 2015 03:47:08 -0400 Received: from mta-out1.inet.fi ([62.71.2.227]:42479 "EHLO jenni2.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751378AbbEKHrG (ORCPT ); Mon, 11 May 2015 03:47:06 -0400 Date: Mon, 11 May 2015 10:46:31 +0300 From: "Kirill A. Shutemov" To: "Aneesh Kumar K.V" 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. Message-ID: <20150511074631.GA10974@node.dhcp.inet.fi> References: <1431325561-21396-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1431325561-21396-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1648 Lines: 35 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@ ? -- Kirill A. Shutemov -- 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/