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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 C3646C433ED for ; Mon, 19 Apr 2021 07:04:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A8E996101C for ; Mon, 19 Apr 2021 07:04:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237580AbhDSHFC (ORCPT ); Mon, 19 Apr 2021 03:05:02 -0400 Received: from mga03.intel.com ([134.134.136.65]:44012 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237536AbhDSHFB (ORCPT ); Mon, 19 Apr 2021 03:05:01 -0400 IronPort-SDR: yKiEiJZ48TAJtM6rwLPR0LdxxjhM5UcXvKcrATZmw+HT943rCX0LIupXQbqAsJ5EV+hezSznfp usAI0jg3mr2w== X-IronPort-AV: E=McAfee;i="6200,9189,9958"; a="195307314" X-IronPort-AV: E=Sophos;i="5.82,233,1613462400"; d="scan'208";a="195307314" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 00:04:32 -0700 IronPort-SDR: MUlDaBI5HASs6JlvlWKixauRiUFFsY672fNMw7FpcTRvWpYdDHMy0czmht7QiDdWJewXa95YlQ gR17TXsXHsuw== X-IronPort-AV: E=Sophos;i="5.82,233,1613462400"; d="scan'208";a="534047464" Received: from yhuang6-desk1.sh.intel.com (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 00:04:28 -0700 From: "Huang, Ying" To: Miaohe Lin Cc: , , , , , , , , , , , , Subject: Re: [PATCH v2 5/5] mm/shmem: fix shmem_swapin() race with swapoff References: <20210417094039.51711-1-linmiaohe@huawei.com> <20210417094039.51711-6-linmiaohe@huawei.com> <87r1j7kok3.fsf@yhuang6-desk1.ccr.corp.intel.com> Date: Mon, 19 Apr 2021 15:04:11 +0800 In-Reply-To: (Miaohe Lin's message of "Mon, 19 Apr 2021 14:49:47 +0800") Message-ID: <87h7k24uxg.fsf@yhuang6-desk1.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Miaohe Lin writes: > On 2021/4/19 10:15, Huang, Ying wrote: >> Miaohe Lin writes: >> >>> When I was investigating the swap code, I found the below possible race >>> window: >>> >>> CPU 1 CPU 2 >>> ----- ----- >>> shmem_swapin >>> swap_cluster_readahead >>> if (likely(si->flags & (SWP_BLKDEV | SWP_FS_OPS))) { >>> swapoff >>> si->flags &= ~SWP_VALID; >>> .. >>> synchronize_rcu(); >>> .. >> >> You have removed these code in the previous patches of the series. And >> they are not relevant in this patch. > > Yes, I should change these. Thanks. > >> >>> si->swap_file = NULL; >>> struct inode *inode = si->swap_file->f_mapping->host;[oops!] >>> >>> Close this race window by using get/put_swap_device() to guard against >>> concurrent swapoff. >>> >>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") >> >> No. This isn't the commit that introduces the race condition. Please >> recheck your git blame result. >> > > I think this is really hard to find exact commit. I used git blame and found > this race should be existed when this is introduced. Any suggestion ? > Thanks. I think the commit that introduces the race condition is commit 8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not") Best Regards, Huang, Ying >> Best Regards, >> Huang, Ying >> >>> Signed-off-by: Miaohe Lin >>> --- >>> mm/shmem.c | 6 ++++++ >>> 1 file changed, 6 insertions(+) >>> >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index 26c76b13ad23..936ba5595297 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -1492,15 +1492,21 @@ static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma) >>> static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp, >>> struct shmem_inode_info *info, pgoff_t index) >>> { >>> + struct swap_info_struct *si; >>> struct vm_area_struct pvma; >>> struct page *page; >>> struct vm_fault vmf = { >>> .vma = &pvma, >>> }; >>> >>> + /* Prevent swapoff from happening to us. */ >>> + si = get_swap_device(swap); >>> + if (unlikely(!si)) >>> + return NULL; >>> shmem_pseudo_vma_init(&pvma, info, index); >>> page = swap_cluster_readahead(swap, gfp, &vmf); >>> shmem_pseudo_vma_destroy(&pvma); >>> + put_swap_device(si); >>> >>> return page; >>> } >> . >>