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 4207BC43460 for ; Sun, 25 Apr 2021 03:07:22 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B3132611C2 for ; Sun, 25 Apr 2021 03:07:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B3132611C2 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 D31B16B0036; Sat, 24 Apr 2021 23:07:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CB9976B006C; Sat, 24 Apr 2021 23:07:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B32AE6B006E; Sat, 24 Apr 2021 23:07:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0061.hostedemail.com [216.40.44.61]) by kanga.kvack.org (Postfix) with ESMTP id 9364E6B0036 for ; Sat, 24 Apr 2021 23:07:20 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 3C9F01802EFE1 for ; Sun, 25 Apr 2021 03:07:20 +0000 (UTC) X-FDA: 78069403440.05.F531966 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf09.hostedemail.com (Postfix) with ESMTP id 63533600010F for ; Sun, 25 Apr 2021 03:07:11 +0000 (UTC) IronPort-SDR: 92MDdesrzBvPXVnPjyH2gHvr8hXatuaYXmcI2SWNZ1RP/22KAcTBqDW/mtAf398EsvdO3qxr01 9lI4FlvRprEA== X-IronPort-AV: E=McAfee;i="6200,9189,9964"; a="196267500" X-IronPort-AV: E=Sophos;i="5.82,249,1613462400"; d="scan'208";a="196267500" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Apr 2021 20:07:14 -0700 IronPort-SDR: tb7Uxd0r54Hy4tnkUnO2ZpI1EabmeQSPKX52feURX78+7Q0v31a3MwON9PupyowYQUzYq5MUek DxIYxI/RSccw== X-IronPort-AV: E=Sophos;i="5.82,249,1613462400"; d="scan'208";a="422203786" Received: from yhuang6-desk1.sh.intel.com (HELO yhuang6-desk1.ccr.corp.intel.com) ([10.239.13.1]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Apr 2021 20:07:09 -0700 From: "Huang, Ying" To: Miaohe Lin Cc: , , , , , , , , , , , , , , Subject: Re: [PATCH v4 4/4] mm/shmem: fix shmem_swapin() race with swapoff References: <20210425023806.3537283-1-linmiaohe@huawei.com> <20210425023806.3537283-5-linmiaohe@huawei.com> Date: Sun, 25 Apr 2021 11:07:07 +0800 In-Reply-To: <20210425023806.3537283-5-linmiaohe@huawei.com> (Miaohe Lin's message of "Sun, 25 Apr 2021 10:38:06 +0800") Message-ID: <87bla3xdt0.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-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 63533600010F X-Stat-Signature: uhijeqoje6dfsr51z4dya164xs3gacz8 Received-SPF: none (intel.com>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=mga03.intel.com; client-ip=134.134.136.65 X-HE-DKIM-Result: none/none X-HE-Tag: 1619320031-365229 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 > ----- ----- > 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 | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 26c76b13ad23..be388d0cf8b5 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 (unlikely(!si)) { > + error = EINVAL; > + goto failed; > + } > /* Look it up and read it in.. */ > page = lookup_swap_cache(swap, NULL, 0); > if (!page) { > @@ -1720,6 +1727,7 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, > goto failed; > } > } > + put_swap_device(si); I think it's better to put_swap_device() just before returning from the function. It's not a big issue to slow down swapoff() a little. And this will make the logic easier to be understood. Best Regards, Huang, Ying > > /* We have to do this with page locked to prevent races */ > lock_page(page); > @@ -1775,6 +1783,9 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index, > put_page(page); > } > > + if (si) > + put_swap_device(si); > + > return error; > }