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=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 80F6DC433ED for ; Mon, 19 Apr 2021 08:18:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EAB996101C for ; Mon, 19 Apr 2021 08:18:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EAB996101C 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 7612A6B0036; Mon, 19 Apr 2021 04:18:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6E8E76B006E; Mon, 19 Apr 2021 04:18:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 58A3B6B0070; Mon, 19 Apr 2021 04:18:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0059.hostedemail.com [216.40.44.59]) by kanga.kvack.org (Postfix) with ESMTP id 3D0576B0036 for ; Mon, 19 Apr 2021 04:18:44 -0400 (EDT) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id E4DAA68AE for ; Mon, 19 Apr 2021 08:18:43 +0000 (UTC) X-FDA: 78048415326.22.47AA60E Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) by imf23.hostedemail.com (Postfix) with ESMTP id F134FA000391 for ; Mon, 19 Apr 2021 08:18:40 +0000 (UTC) Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4FP05G0WpszqTdv; Mon, 19 Apr 2021 16:16:18 +0800 (CST) Received: from [10.174.178.5] (10.174.178.5) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.498.0; Mon, 19 Apr 2021 16:18:35 +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> <41a33c84-f878-8dab-a1d0-4aea3a1fc739@huawei.com> <877dky4t7b.fsf@yhuang6-desk1.ccr.corp.intel.com> From: Miaohe Lin Message-ID: Date: Mon, 19 Apr 2021 16:18:34 +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: <877dky4t7b.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-Server: rspam01 X-Rspamd-Queue-Id: F134FA000391 X-Stat-Signature: 4ybkx38889fhrsym64dkacfcgx59597x Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf23; identity=mailfrom; envelope-from=""; helo=szxga05-in.huawei.com; client-ip=45.249.212.191 X-HE-DKIM-Result: none/none X-HE-Tag: 1618820320-760359 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 15:41, Huang, Ying wrote: > Miaohe Lin writes: > >> 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. > > No. swap_readpage() in swap_cluster_readahead() is OK. Because > __read_swap_cache_async() is called before that, so the swap entry will > be marked with SWAP_HAS_CACHE, and page will be locked. > Oh... I missed this. Many thanks for your remind. > Best Regards, > Huang, Ying > >>> 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; >>>>>> } >>>>> . >>>>> >>> . >>> > . >