From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754866AbcDKMqe (ORCPT ); Mon, 11 Apr 2016 08:46:34 -0400 Received: from mail-pa0-f49.google.com ([209.85.220.49]:36071 "EHLO mail-pa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754209AbcDKMqc (ORCPT ); Mon, 11 Apr 2016 08:46:32 -0400 Subject: Re: [PATCH 03/10] mm/hugetlb: Protect follow_huge_(pud|pgd) functions from race To: Anshuman Khandual , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <1460007464-26726-1-git-send-email-khandual@linux.vnet.ibm.com> <1460007464-26726-4-git-send-email-khandual@linux.vnet.ibm.com> <570627C9.5030105@gmail.com> <570B3897.6040804@linux.vnet.ibm.com> Cc: hughd@google.com, dave.hansen@intel.com, aneesh.kumar@linux.vnet.ibm.com, kirill@shutemov.name, n-horiguchi@ah.jp.nec.com, mgorman@techsingularity.net, akpm@linux-foundation.org From: Balbir Singh Message-ID: <570B9C93.5050507@gmail.com> Date: Mon, 11 Apr 2016 22:46:11 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 MIME-Version: 1.0 In-Reply-To: <570B3897.6040804@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/04/16 15:39, Anshuman Khandual wrote: > On 04/07/2016 02:56 PM, Balbir Singh wrote: >> >> On 07/04/16 15:37, Anshuman Khandual wrote: >>>> follow_huge_(pmd|pud|pgd) functions are used to walk the page table and >>>> fetch the page struct during 'follow_page_mask' call. There are possible >>>> race conditions faced by these functions which arise out of simultaneous >>>> calls of move_pages() and freeing of huge pages. This was fixed partly >>>> by the previous commit e66f17ff7177 ("mm/hugetlb: take page table lock >>>> in follow_huge_pmd()") for only PMD based huge pages. >>>> >>>> After implementing similar logic, functions like follow_huge_(pud|pgd) >>>> are now safe from above mentioned race conditions and also can support >>>> FOLL_GET. Generic version of the function 'follow_huge_addr' has been >>>> left as it is and its upto the architecture to decide on it. >>>> >>>> Signed-off-by: Anshuman Khandual >>>> --- >>>> include/linux/mm.h | 33 +++++++++++++++++++++++++++ >>>> mm/hugetlb.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++-------- >>>> 2 files changed, 91 insertions(+), 9 deletions(-) >>>> >>>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>>> index ffcff53..734182a 100644 >>>> --- a/include/linux/mm.h >>>> +++ b/include/linux/mm.h >>>> @@ -1751,6 +1751,19 @@ static inline void pgtable_page_dtor(struct page *page) >>>> NULL: pte_offset_kernel(pmd, address)) >>>> >>>> #if USE_SPLIT_PMD_PTLOCKS >> Do we still use USE_SPLIT_PMD_PTLOCKS? I think its good enough. with pgd's >> we are likely to use the same locks and the split nature may not be really >> split. >> > > Sorry Balbir, did not get what you asked. Can you please elaborate on > this ? > What I meant is that do we need SPLIT_PUD_PTLOCKS for example? I don't think we do Balbir