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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 47F7CC00449 for ; Mon, 8 Oct 2018 06:23:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F3A4D20841 for ; Mon, 8 Oct 2018 06:23:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F3A4D20841 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726445AbeJHNd2 (ORCPT ); Mon, 8 Oct 2018 09:33:28 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:43310 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725857AbeJHNd2 (ORCPT ); Mon, 8 Oct 2018 09:33:28 -0400 Received: from fsav301.sakura.ne.jp (fsav301.sakura.ne.jp [153.120.85.132]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w986Mcsv030411; Mon, 8 Oct 2018 15:22:38 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav301.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav301.sakura.ne.jp); Mon, 08 Oct 2018 15:22:38 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav301.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157066051.bbtec.net [60.157.66.51]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w986Mc4C030406 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 8 Oct 2018 15:22:38 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes sharing mm To: ytk.lee@samsung.com, "mhocko@kernel.org" , "mhocko@suse.com" Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" References: <20181008011931epcms1p82dd01b7e5c067ea99946418bc97de46a@epcms1p8> <20181008061407epcms1p519703ae6373a770160c8f912c7aa9521@epcms1p5> From: Tetsuo Handa Message-ID: <67eedc4c-7afa-e845-6c88-9716fd820de6@i-love.sakura.ne.jp> Date: Mon, 8 Oct 2018 15:22:37 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181008061407epcms1p519703ae6373a770160c8f912c7aa9521@epcms1p5> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/10/08 15:14, Yong-Taek Lee wrote: >> On 2018/10/08 10:19, Yong-Taek Lee wrote: >>> @@ -1056,6 +1056,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) >>> struct mm_struct *mm = NULL; >>> struct task_struct *task; >>> int err = 0; >>> + int mm_users = 0; >>> >>> task = get_proc_task(file_inode(file)); >>> if (!task) >>> @@ -1092,7 +1093,8 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) >>> struct task_struct *p = find_lock_task_mm(task); >>> >>> if (p) { >>> - if (atomic_read(&p->mm->mm_users) > 1) { >>> + mm_users = atomic_read(&p->mm->mm_users); >>> + if ((mm_users > 1) && (mm_users != get_nr_threads(p))) { >> >> How can this work (even before this patch)? When clone(CLONE_VM without CLONE_THREAD/CLONE_SIGHAND) >> is requested, copy_process() calls copy_signal() in order to copy sig->oom_score_adj and >> sig->oom_score_adj_min before calling copy_mm() in order to increment mm->mm_users, doesn't it? >> Then, we will get two different "struct signal_struct" with different oom_score_adj/oom_score_adj_min >> but one "struct mm_struct" shared by two thread groups. >> > > Are you talking about race between __set_oom_adj and copy_process? > If so, i agree with your opinion. It can not set oom_score_adj properly for copied process if __set_oom_adj > check mm_users before copy_process calls copy_mm after copy_signal. Please correct me if i misunderstood anything. You understand it correctly. Reversing copy_signal() and copy_mm() is not sufficient either. We need to use a read/write lock (read lock for copy_process() and write lock for __set_oom_adj()) in order to make sure that the thread created by clone() becomes reachable from for_each_process() path in __set_oom_adj(). > >>> mm = p->mm; >>> atomic_inc(&mm->mm_count); >>> } >