Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752632AbbEKG1T (ORCPT ); Mon, 11 May 2015 02:27:19 -0400 Received: from e23smtp04.au.ibm.com ([202.81.31.146]:41633 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752398AbbEKG1Q (ORCPT ); Mon, 11 May 2015 02:27:16 -0400 From: "Aneesh Kumar K.V" To: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, kirill.shutemov@linux.intel.com, aarcange@redhat.com, akpm@linux-foundation.org Cc: linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Aneesh Kumar K.V" Subject: [PATCH V3] powerpc/thp: Serialize pmd clear against a linux page table walk. Date: Mon, 11 May 2015 11:56:01 +0530 Message-Id: <1431325561-21396-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> X-Mailer: git-send-email 2.1.4 X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15051106-0013-0000-0000-0000013B169D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2562 Lines: 61 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 --- Changes from V2: * Drop the cleanup patch Will this as a separate patch and not bug fix. * Update commit message arch/powerpc/mm/pgtable_64.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c index b651179ac4da..1325be89e670 100644 --- a/arch/powerpc/mm/pgtable_64.c +++ b/arch/powerpc/mm/pgtable_64.c @@ -845,6 +845,17 @@ pmd_t pmdp_get_and_clear(struct mm_struct *mm, * hash fault look at them. */ memset(pgtable, 0, PTE_FRAG_SIZE); + /* + * 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. + */ + kick_all_cpus_sync(); return old_pmd; } -- 2.1.4 -- 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/