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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B341CC761A6 for ; Mon, 3 Apr 2023 08:02:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231781AbjDCICk (ORCPT ); Mon, 3 Apr 2023 04:02:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55728 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229659AbjDCICj (ORCPT ); Mon, 3 Apr 2023 04:02:39 -0400 Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0DFC41725; Mon, 3 Apr 2023 01:02:37 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R831e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046059;MF=rongwei.wang@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0VfFRiwW_1680508954; Received: from 30.24.98.140(mailfrom:rongwei.wang@linux.alibaba.com fp:SMTPD_---0VfFRiwW_1680508954) by smtp.aliyun-inc.com; Mon, 03 Apr 2023 16:02:35 +0800 Message-ID: <4301a7be-354f-183d-a828-01445434a1b3@linux.alibaba.com> Date: Mon, 3 Apr 2023 16:02:34 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/swap: fix swap_info_struct race between swapoff and get_swap_pages() Content-Language: en-US To: Matthew Wilcox Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20230401221920.57986-1-rongwei.wang@linux.alibaba.com> From: Rongwei Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 4/3/23 12:10 PM, Matthew Wilcox wrote: > On Sun, Apr 02, 2023 at 06:19:20AM +0800, Rongwei Wang wrote: >> Without this modification, a core will wait (mostly) >> 'swap_info_struct->lock' when completing >> 'del_from_avail_list(p)'. Immediately, other cores >> soon calling 'add_to_avail_list()' to add the same >> object again when acquiring the lock that released >> by former. It's not the desired result but exists >> indeed. This case can be described as below: > This feels like a very verbose way of saying > > "The si->lock must be held when deleting the si from the > available list. Otherwise, another thread can re-add the > si to the available list, which can lead to memory corruption. > The only place we have found where this happens is in the > swapoff path." It looks better than mine. Sorry for my confusing description, it will be fixed in the next version. > >> +++ b/mm/swapfile.c >> @@ -2610,8 +2610,12 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) >> spin_unlock(&swap_lock); >> goto out_dput; >> } >> - del_from_avail_list(p); >> + /* >> + * Here lock is used to protect deleting and SWP_WRITEOK clearing >> + * can be seen concurrently. >> + */ > This comment isn't necessary. But I would add a lockdep assert inside > __del_from_avail_list() that p->lock is held. Thanks. Actually, I have this line in previous test version, but delete for saving one line of code. I will update here as you said. Thanks for your time. > >> spin_lock(&p->lock); >> + del_from_avail_list(p); >> if (p->prio < 0) { >> struct swap_info_struct *si = p; >> int nid; >> -- >> 2.27.0 >> >>