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 41B87C433ED for ; Mon, 19 Apr 2021 07:14:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A3BA46102A for ; Mon, 19 Apr 2021 07:14:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A3BA46102A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 18F036B0036; Mon, 19 Apr 2021 03:14:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 13F9A6B006E; Mon, 19 Apr 2021 03:14:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 006926B0070; Mon, 19 Apr 2021 03:14:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0126.hostedemail.com [216.40.44.126]) by kanga.kvack.org (Postfix) with ESMTP id D9AD06B0036 for ; Mon, 19 Apr 2021 03:14:17 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 8B05A5DF9 for ; Mon, 19 Apr 2021 07:14:17 +0000 (UTC) X-FDA: 78048252954.14.D4A6DC5 Received: from szxga06-in.huawei.com (szxga06-in.huawei.com [45.249.212.32]) by imf14.hostedemail.com (Postfix) with ESMTP id 3858AC0007DB for ; Mon, 19 Apr 2021 07:14:06 +0000 (UTC) Received: from DGGEMS406-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4FNygP4Gk3zlYyH; Mon, 19 Apr 2021 15:12:17 +0800 (CST) Received: from [10.174.178.5] (10.174.178.5) by DGGEMS406-HUB.china.huawei.com (10.3.19.206) with Microsoft SMTP Server id 14.3.498.0; Mon, 19 Apr 2021 15:14:10 +0800 Subject: Re: [PATCH v2 5/5] mm/shmem: fix shmem_swapin() race with swapoff To: "Huang, Ying" CC: , , , , , , , , , , , , References: <20210417094039.51711-1-linmiaohe@huawei.com> <20210417094039.51711-6-linmiaohe@huawei.com> <87r1j7kok3.fsf@yhuang6-desk1.ccr.corp.intel.com> <87h7k24uxg.fsf@yhuang6-desk1.ccr.corp.intel.com> From: Miaohe Lin Message-ID: <41a33c84-f878-8dab-a1d0-4aea3a1fc739@huawei.com> Date: Mon, 19 Apr 2021 15:14:10 +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: <87h7k24uxg.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: [10.174.178.5] X-CFilter-Loop: Reflected X-Rspamd-Queue-Id: 3858AC0007DB X-Stat-Signature: 4fstq6b6jzzjj48pnwt8tuqxzfmr43b9 X-Rspamd-Server: rspam02 Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf14; identity=mailfrom; envelope-from=""; helo=szxga06-in.huawei.com; client-ip=45.249.212.32 X-HE-DKIM-Result: none/none X-HE-Tag: 1618816446-148705 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021/4/19 15:04, Huang, Ying wrote: > 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") > Thanks. The commit log only describes one race condition. And for that one, this should be correct Fixes tag. But there are still many other race conditions inside swap_cluster_readahead, such as swap_readpage() called from swap_cluster_readahead. This tag could not cover the all race windows. > 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; >>>> } >>> . >>> > . >