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=-13.8 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 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 5B7D2C433B4 for ; Mon, 19 Apr 2021 02:24:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E2F5260FF3 for ; Mon, 19 Apr 2021 02:24:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E2F5260FF3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 76BC96B0036; Sun, 18 Apr 2021 22:24:08 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 742396B006E; Sun, 18 Apr 2021 22:24:08 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 609E46B0070; Sun, 18 Apr 2021 22:24:08 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0049.hostedemail.com [216.40.44.49]) by kanga.kvack.org (Postfix) with ESMTP id 3CFCB6B0036 for ; Sun, 18 Apr 2021 22:24:08 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id E6771180AD837 for ; Mon, 19 Apr 2021 02:24:07 +0000 (UTC) X-FDA: 78047521734.17.D39FB2C Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by imf18.hostedemail.com (Postfix) with ESMTP id 78C752000242 for ; Mon, 19 Apr 2021 02:24:08 +0000 (UTC) IronPort-SDR: TX0gJpNBsqmc7nojztxHJ+9d9xMoaZh+j/TQqWRMiNRWPpMI6VOKsMwp0U1eVtdc/RN4mVwFC0 sS8DZO5zLUVw== X-IronPort-AV: E=McAfee;i="6200,9189,9958"; a="280581352" X-IronPort-AV: E=Sophos;i="5.82,232,1613462400"; d="scan'208";a="280581352" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2021 19:24:05 -0700 IronPort-SDR: E2tx3KbQIVp4eQDaF/1C81uzKqFwF3rgmB5bbYuJmKs739v2n5aEFQ0H3Et2HtNjIiYUmSZXeJ Ld9oLPG5XsmA== X-IronPort-AV: E=Sophos;i="5.82,232,1613462400"; d="scan'208";a="400480351" Received: from yhuang6-desk1.sh.intel.com (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2021 19:24:01 -0700 From: "Huang, Ying" To: Miaohe Lin Cc: , , , , , , , , , , , , Subject: Re: [PATCH v2 3/5] swap: fix do_swap_page() race with swapoff References: <20210417094039.51711-1-linmiaohe@huawei.com> <20210417094039.51711-4-linmiaohe@huawei.com> Date: Mon, 19 Apr 2021 10:23:59 +0800 In-Reply-To: <20210417094039.51711-4-linmiaohe@huawei.com> (Miaohe Lin's message of "Sat, 17 Apr 2021 05:40:37 -0400") Message-ID: <87k0ozko5c.fsf@yhuang6-desk1.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Stat-Signature: d1dgj69yuemcam3etw6mgg6hsin1egm9 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 78C752000242 Received-SPF: none (intel.com>: No applicable sender policy available) receiver=imf18; identity=mailfrom; envelope-from=""; helo=mga05.intel.com; client-ip=192.55.52.43 X-HE-DKIM-Result: none/none X-HE-Tag: 1618799048-110444 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: Miaohe Lin writes: > When I was investigating the swap code, I found the below possible race > window: > > CPU 1 CPU 2 > ----- ----- > do_swap_page This is OK for swap cache cases. So if (data_race(si->flags & SWP_SYNCHRONOUS_IO)) should be shown here. > 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). I still suggest to squash PATCH 1-3, at least PATCH 1-2. That will change the relevant code together and make it easier to review. Best Regards, 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; > }