From patchwork Sat Apr 17 09:40:37 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Miaohe Lin X-Patchwork-Id: 12209621 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=-16.7 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,USER_AGENT_GIT 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 3EB4CC43461 for ; Sat, 17 Apr 2021 09:42:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DBE6561026 for ; Sat, 17 Apr 2021 09:41:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DBE6561026 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 46DB46B0073; Sat, 17 Apr 2021 05:41:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 41DBC6B0074; Sat, 17 Apr 2021 05:41:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 29CA76B0075; Sat, 17 Apr 2021 05:41:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0037.hostedemail.com [216.40.44.37]) by kanga.kvack.org (Postfix) with ESMTP id F2BF46B0073 for ; Sat, 17 Apr 2021 05:41:54 -0400 (EDT) Received: from smtpin36.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id B1F55180ACF7F for ; Sat, 17 Apr 2021 09:41:54 +0000 (UTC) X-FDA: 78041367348.36.03F2569 Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) by imf30.hostedemail.com (Postfix) with ESMTP id 96F9DE00010B for ; Sat, 17 Apr 2021 09:41:40 +0000 (UTC) Received: from DGGEMS410-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4FMp2C1LWnzyPLG; Sat, 17 Apr 2021 17:39:31 +0800 (CST) Received: from huawei.com (10.175.104.175) by DGGEMS410-HUB.china.huawei.com (10.3.19.210) with Microsoft SMTP Server id 14.3.498.0; Sat, 17 Apr 2021 17:41:39 +0800 From: Miaohe Lin To: CC: , , , , , , , , , , , , , Subject: [PATCH v2 3/5] swap: fix do_swap_page() race with swapoff Date: Sat, 17 Apr 2021 05:40:37 -0400 Message-ID: <20210417094039.51711-4-linmiaohe@huawei.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20210417094039.51711-1-linmiaohe@huawei.com> References: <20210417094039.51711-1-linmiaohe@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.175.104.175] X-CFilter-Loop: Reflected X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 96F9DE00010B X-Stat-Signature: sbjbjf86b1w1us6szqm3gpp9xa333hcm Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=szxga05-in.huawei.com; client-ip=45.249.212.191 X-HE-DKIM-Result: none/none X-HE-Tag: 1618652500-286281 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: When I was investigating the swap code, I found the below possible race window: CPU 1 CPU 2 ----- ----- do_swap_page swap_readpage(skip swap cache case) if (data_race(sis->flags & SWP_FS_OPS)) { swapoff p->flags = &= ~SWP_VALID; .. synchronize_rcu(); .. p->swap_file = NULL; struct file *swap_file = sis->swap_file; struct address_space *mapping = swap_file->f_mapping;[oops!] Note that for the pages that are swapped in through swap cache, this isn't an issue. Because the page is locked, and the swap entry will be marked with SWAP_HAS_CACHE, so swapoff() can not proceed until the page has been unlocked. Using current get/put_swap_device() to guard against concurrent swapoff for swap_readpage() looks terrible because swap_readpage() may take really long time. And this race may not be really pernicious because swapoff is usually done when system shutdown only. To reduce the performance overhead on the hot-path as much as possible, it appears we can use the percpu_ref to close this race window(as suggested by Huang, Ying). Fixes: 0bcac06f27d7 ("mm,swap: skip swapcache for swapin of synchronous device") Reported-by: kernel test robot (auto build test ERROR) Signed-off-by: Miaohe Lin --- include/linux/swap.h | 9 +++++++++ mm/memory.c | 9 +++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/swap.h b/include/linux/swap.h index 993693b38109..523c2411a135 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -528,6 +528,15 @@ static inline struct swap_info_struct *swp_swap_info(swp_entry_t entry) return NULL; } +static inline struct swap_info_struct *get_swap_device(swp_entry_t entry) +{ + return NULL; +} + +static inline void put_swap_device(struct swap_info_struct *si) +{ +} + #define swap_address_space(entry) (NULL) #define get_nr_swap_pages() 0L #define total_swap_pages 0L diff --git a/mm/memory.c b/mm/memory.c index 27014c3bde9f..7a2fe12cf641 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3311,6 +3311,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; struct page *page = NULL, *swapcache; + struct swap_info_struct *si = NULL; swp_entry_t entry; pte_t pte; int locked; @@ -3338,6 +3339,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) goto out; } + /* Prevent swapoff from happening to us. */ + si = get_swap_device(entry); + if (unlikely(!si)) + goto out; delayacct_set_flag(current, DELAYACCT_PF_SWAPIN); page = lookup_swap_cache(entry, vma, vmf->address); @@ -3514,6 +3519,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) unlock: pte_unmap_unlock(vmf->pte, vmf->ptl); out: + if (si) + put_swap_device(si); return ret; out_nomap: pte_unmap_unlock(vmf->pte, vmf->ptl); @@ -3525,6 +3532,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) unlock_page(swapcache); put_page(swapcache); } + if (si) + put_swap_device(si); return ret; }