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=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 C32F1C433ED for ; Mon, 26 Apr 2021 07:05:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8CA5160E0C for ; Mon, 26 Apr 2021 07:05:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231984AbhDZHFy (ORCPT ); Mon, 26 Apr 2021 03:05:54 -0400 Received: from szxga07-in.huawei.com ([45.249.212.35]:17817 "EHLO szxga07-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231616AbhDZHFx (ORCPT ); Mon, 26 Apr 2021 03:05:53 -0400 Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4FTG7731QYzBryB; Mon, 26 Apr 2021 15:02:43 +0800 (CST) Received: from [10.174.176.174] (10.174.176.174) by DGGEMS407-HUB.china.huawei.com (10.3.19.207) with Microsoft SMTP Server id 14.3.498.0; Mon, 26 Apr 2021 15:05:08 +0800 Subject: Re: [PATCH v5 4/4] mm/shmem: fix shmem_swapin() race with swapoff To: Yu Zhao CC: Andrew Morton , Huang Ying , , Tim Chen , Hugh Dickins , "Johannes Weiner" , Michal Hocko , Joonsoo Kim , , Matthew Wilcox , Minchan Kim , Wei Yang , Yang Shi , "David Hildenbrand" , linux-kernel , Linux-MM References: <20210425095419.3830298-1-linmiaohe@huawei.com> <20210425095419.3830298-5-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <2408403a-a0c3-b87e-b7ab-46cbaf35fb47@huawei.com> Date: Mon, 26 Apr 2021 15:05:07 +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: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.174] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/4/26 14:53, Yu Zhao wrote: > On Sun, Apr 25, 2021 at 3:54 AM Miaohe Lin wrote: >> >> 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->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: 8fd2e0b505d1 ("mm: swap: check if swap backing device is congested or not") >> Signed-off-by: Miaohe Lin >> --- >> mm/shmem.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 26c76b13ad23..2dafd65b0b42 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -1696,6 +1696,7 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, >> struct address_space *mapping = inode->i_mapping; >> struct shmem_inode_info *info = SHMEM_I(inode); >> struct mm_struct *charge_mm = vma ? vma->vm_mm : current->mm; >> + struct swap_info_struct *si; >> struct page *page; >> swp_entry_t swap; >> int error; >> @@ -1704,6 +1705,12 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, >> swap = radix_to_swp_entry(*pagep); >> *pagep = NULL; >> >> + /* Prevent swapoff from happening to us. */ >> + si = get_swap_device(swap); >> + if (!si) { >> + error = EINVAL; >> + goto failed; >> + } > > page is uninitialized? > Sorry, my overlook! Compiler should have complained about it but there is none... Many thanks for pointing this out! Will fix it in next version. >> /* Look it up and read it in.. */ >> page = lookup_swap_cache(swap, NULL, 0); >> if (!page) { >> @@ -1765,6 +1772,8 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, >> swap_free(swap); >> >> *pagep = page; >> + if (si) >> + put_swap_device(si); >> return 0; >> failed: >> if (!shmem_confirm_swap(mapping, index, swap)) >> @@ -1775,6 +1784,9 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, >> put_page(page); >> } >> >> + if (si) >> + put_swap_device(si); >> + >> return error; >> } >> >> -- >> 2.23.0 >> >> > . >