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 X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 135E5C433ED for ; Mon, 12 Apr 2021 03:18:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6AE56103D for ; Mon, 12 Apr 2021 03:18:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236080AbhDLDSR (ORCPT ); Sun, 11 Apr 2021 23:18:17 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:16522 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235095AbhDLDSP (ORCPT ); Sun, 11 Apr 2021 23:18:15 -0400 Received: from DGGEMS410-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4FJYky441qzPqGT; Mon, 12 Apr 2021 11:15:06 +0800 (CST) Received: from [10.174.176.162] (10.174.176.162) by DGGEMS410-HUB.china.huawei.com (10.3.19.210) with Microsoft SMTP Server id 14.3.498.0; Mon, 12 Apr 2021 11:17:54 +0800 Subject: Re: [PATCH 4/5] mm/swap_state: fix potential faulted in race in swap_ra_info() To: "Huang, Ying" CC: , , , , , , , , , , , , References: <20210408130820.48233-1-linmiaohe@huawei.com> <20210408130820.48233-5-linmiaohe@huawei.com> <874kgfyh85.fsf@yhuang6-desk1.ccr.corp.intel.com> <87v98swcd6.fsf@yhuang6-desk1.ccr.corp.intel.com> From: Miaohe Lin Message-ID: <55611ebf-e608-87df-c86a-e6a19bab96ca@huawei.com> Date: Mon, 12 Apr 2021 11:17:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <87v98swcd6.fsf@yhuang6-desk1.ccr.corp.intel.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.162] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/4/12 8:55, Huang, Ying wrote: > Miaohe Lin writes: > >> On 2021/4/9 16:50, Huang, Ying wrote: >>> Miaohe Lin writes: >>> >>>> While we released the pte lock, somebody else might faulted in this pte. >>>> So we should check whether it's swap pte first to guard against such race >>>> or swp_type would be unexpected. And we can also avoid some unnecessary >>>> readahead cpu cycles possibly. >>>> >>>> Fixes: ec560175c0b6 ("mm, swap: VMA based swap readahead") >>>> Signed-off-by: Miaohe Lin >>>> --- >>>> mm/swap_state.c | 13 +++++++++---- >>>> 1 file changed, 9 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/mm/swap_state.c b/mm/swap_state.c >>>> index 709c260d644a..3bf0d0c297bc 100644 >>>> --- a/mm/swap_state.c >>>> +++ b/mm/swap_state.c >>>> @@ -724,10 +724,10 @@ static void swap_ra_info(struct vm_fault *vmf, >>>> { >>>> struct vm_area_struct *vma = vmf->vma; >>>> unsigned long ra_val; >>>> - swp_entry_t entry; >>>> + swp_entry_t swap_entry; >>>> unsigned long faddr, pfn, fpfn; >>>> unsigned long start, end; >>>> - pte_t *pte, *orig_pte; >>>> + pte_t *pte, *orig_pte, entry; >>>> unsigned int max_win, hits, prev_win, win, left; >>>> #ifndef CONFIG_64BIT >>>> pte_t *tpte; >>>> @@ -742,8 +742,13 @@ static void swap_ra_info(struct vm_fault *vmf, >>>> >>>> faddr = vmf->address; >>>> orig_pte = pte = pte_offset_map(vmf->pmd, faddr); >>>> - entry = pte_to_swp_entry(*pte); >>>> - if ((unlikely(non_swap_entry(entry)))) { >>>> + entry = *pte; >>>> + if (unlikely(!is_swap_pte(entry))) { >>>> + pte_unmap(orig_pte); >>>> + return; >>>> + } >>>> + swap_entry = pte_to_swp_entry(entry); >>>> + if ((unlikely(non_swap_entry(swap_entry)))) { >>>> pte_unmap(orig_pte); >>>> return; >>>> } >>> >>> This isn't a real issue. entry or swap_entry isn't used in this >> >> Agree. It seems the entry or swap_entry here is just used for check whether >> pte is still valid swap_entry. > > If you check the git history, you will find that the check has been > necessary before. Because the function is used earlier in > do_swap_page() at that time. > I see. Many thanks for explanation. :) > Best Regards, > Huang, Ying > . >