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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 790BCC43462 for ; Tue, 20 Apr 2021 13:31:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 06E0061026 for ; Tue, 20 Apr 2021 13:31:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 06E0061026 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 57E4F6B006C; Tue, 20 Apr 2021 09:31:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5519F6B0072; Tue, 20 Apr 2021 09:31:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 32F5E6B0074; Tue, 20 Apr 2021 09:31:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0229.hostedemail.com [216.40.44.229]) by kanga.kvack.org (Postfix) with ESMTP id 140A66B006C for ; Tue, 20 Apr 2021 09:31:55 -0400 (EDT) Received: from smtpin37.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id C76D1181AEF1E for ; Tue, 20 Apr 2021 13:31:54 +0000 (UTC) X-FDA: 78052833348.37.7EFA500 Received: from szxga07-in.huawei.com (szxga07-in.huawei.com [45.249.212.35]) by imf11.hostedemail.com (Postfix) with ESMTP id 57BA7200027D for ; Tue, 20 Apr 2021 13:31:40 +0000 (UTC) Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4FPl022kKBzBrVQ; Tue, 20 Apr 2021 21:29:22 +0800 (CST) Received: from huawei.com (10.175.104.175) by DGGEMS402-HUB.china.huawei.com (10.3.19.202) with Microsoft SMTP Server id 14.3.498.0; Tue, 20 Apr 2021 21:31:38 +0800 From: Miaohe Lin To: CC: , , , , , , , , , , , , , , Subject: [PATCH v3 2/4] swap: fix do_swap_page() race with swapoff Date: Tue, 20 Apr 2021 09:30:46 -0400 Message-ID: <20210420133048.6773-3-linmiaohe@huawei.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20210420133048.6773-1-linmiaohe@huawei.com> References: <20210420133048.6773-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.175.104.175] X-CFilter-Loop: Reflected X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 57BA7200027D X-Stat-Signature: skfxxrh4hgeonks8mhbcb59yihhkmcbz Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf11; identity=mailfrom; envelope-from=""; helo=szxga07-in.huawei.com; client-ip=45.249.212.35 X-HE-DKIM-Result: none/none X-HE-Tag: 1618925500-383062 Content-Transfer-Encoding: quoted-printable 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 if (data_race(si->flags & SWP_SYNCHRONOUS_IO) swap_readpage if (data_race(sis->flags & SWP_FS_OPS)) { swapoff p->flags &=3D ~SWP_VALID; .. synchronize_rcu(); .. p->swap_file =3D NULL; struct file *swap_file =3D sis->swap_file; struct address_space *mapping =3D 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 f= or swap_readpage() looks terrible because swap_readpage() may take really lo= ng time. And this race may not be really pernicious because swapoff is usual= ly 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 clo= se this race window(as suggested by Huang, Ying). Fixes: 0bcac06f27d7 ("mm,swap: skip swapcache for swapin of synchronous d= evice") 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 c9e7fea10b83..46d51d058d05 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -527,6 +527,15 @@ static inline struct swap_info_struct *swp_swap_info= (swp_entry_t entry) return NULL; } =20 +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 =3D vmf->vma; struct page *page =3D NULL, *swapcache; + struct swap_info_struct *si =3D 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; } =20 + /* Prevent swapoff from happening to us. */ + si =3D get_swap_device(entry); + if (unlikely(!si)) + goto out; =20 delayacct_set_flag(current, DELAYACCT_PF_SWAPIN); page =3D 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; } =20 --=20 2.19.1