From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f200.google.com (mail-pf1-f200.google.com [209.85.210.200]) by kanga.kvack.org (Postfix) with ESMTP id 0829A6B0005 for ; Mon, 8 Oct 2018 04:39:01 -0400 (EDT) Received: by mail-pf1-f200.google.com with SMTP id a64-v6so10632558pfg.16 for ; Mon, 08 Oct 2018 01:39:01 -0700 (PDT) Received: from mailout1.samsung.com (mailout1.samsung.com. [203.254.224.24]) by mx.google.com with ESMTPS id s17-v6si16960132plq.339.2018.10.08.01.38.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 08 Oct 2018 01:38:59 -0700 (PDT) Received: from epcas1p3.samsung.com (unknown [182.195.41.47]) by mailout1.samsung.com (KnoxPortal) with ESMTP id 20181008083857epoutp01e96b582c5a220fb560ff3acbeb9616b7~blWAI5pQw1021510215epoutp01U for ; Mon, 8 Oct 2018 08:38:57 +0000 (GMT) Mime-Version: 1.0 Subject: RE: Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes sharing mm Reply-To: ytk.lee@samsung.com From: Yong-Taek Lee In-Reply-To: <67eedc4c-7afa-e845-6c88-9716fd820de6@i-love.sakura.ne.jp> Message-ID: <20181008083855epcms1p20e691e5a001f3b94b267997c24e91128@epcms1p2> Date: Mon, 08 Oct 2018 17:38:55 +0900 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" References: <67eedc4c-7afa-e845-6c88-9716fd820de6@i-love.sakura.ne.jp> <20181008011931epcms1p82dd01b7e5c067ea99946418bc97de46a@epcms1p8> <20181008061407epcms1p519703ae6373a770160c8f912c7aa9521@epcms1p5> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa , Yong-Taek Lee , "mhocko@kernel.org" , "mhocko@suse.com" Cc: "linux-mm@kvack.org" , "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(). > Thank you for your suggestion. But i think it would be better to seperate to 2 issues. How about think these issues separately because there are no dependency between race issue and my patch. As i already explained, for_each_process path is meaningless if there is only one thread group with many threads(mm_users > 1 but no other thread group sharing same mm). Do you have any other idea to avoid meaningless loop ? >> >>>> mm = p->mm; >>>> atomic_inc(&mm->mm_count); >>>> } >> >