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,URIBL_BLOCKED, 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 8EA72C433ED for ; Fri, 9 Apr 2021 09:00:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5DCC2611BE for ; Fri, 9 Apr 2021 09:00:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231998AbhDIJA0 (ORCPT ); Fri, 9 Apr 2021 05:00:26 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:15996 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231954AbhDIJAW (ORCPT ); Fri, 9 Apr 2021 05:00:22 -0400 Received: from DGGEMS406-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4FGsTw1VVxzvS3c; Fri, 9 Apr 2021 16:57:56 +0800 (CST) Received: from [10.174.179.9] (10.174.179.9) by DGGEMS406-HUB.china.huawei.com (10.3.19.206) with Microsoft SMTP Server id 14.3.498.0; Fri, 9 Apr 2021 17:00:03 +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> From: Miaohe Lin Message-ID: Date: Fri, 9 Apr 2021 17:00:02 +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: <874kgfyh85.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: [10.174.179.9] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > function. And we have enough checking when we really operate the PTE > entries later. But I admit it's confusing. So I suggest to just remove > the checking. We will check it when necessary. Sounds reasonable. Will do it in v2. Many thanks for review and reply! > > Best Regards, > Huang, Ying > . >