From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 202506B0006 for ; Sun, 1 Apr 2018 21:58:33 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id c65so11629522pfa.5 for ; Sun, 01 Apr 2018 18:58:33 -0700 (PDT) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com. [115.124.30.130]) by mx.google.com with ESMTPS id z123si3841240pgz.332.2018.04.01.18.58.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 01 Apr 2018 18:58:31 -0700 (PDT) Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct References: <1522088439-105930-1-git-send-email-yang.shi@linux.alibaba.com> <20180327062939.GV5652@dhcp22.suse.cz> From: Yang Shi Message-ID: Date: Sun, 1 Apr 2018 18:58:07 -0700 MIME-Version: 1.0 In-Reply-To: <20180327062939.GV5652@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: adobriyan@gmail.com, willy@infradead.org, mguzik@redhat.com, gorcunov@openvz.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 3/26/18 11:29 PM, Michal Hocko wrote: > On Tue 27-03-18 02:20:39, Yang Shi wrote: > [...] > The patch looks reasonable to me. Maybe it would be better to be more > explicit about the purpose of the patch. As others noticed, this alone > wouldn't solve the mmap_sem contention issues. I _think_ that if you > were more explicit about the mmap_sem abuse it would trigger less > questions. > > I have just one more question. Now that you are touching this area, > would you be willing to remove the following ugliness? > >> diff --git a/kernel/sys.c b/kernel/sys.c >> index f2289de..17bddd2 100644 >> --- a/kernel/sys.c >> +++ b/kernel/sys.c >> @@ -1959,7 +1959,7 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data >> return error; >> } >> >> - down_write(&mm->mmap_sem); >> + down_read(&mm->mmap_sem); > Why do we need to hold mmap_sem here and call find_vma, when only > PR_SET_MM_ENV_END: is consuming it? I guess we can replace it wit the > new lock and take the mmap_sem only for PR_SET_MM_ENV_END. Sorry for taking a little bit longer to get back since I was traveling. I think all the stuff can be protected by the new arg_lock except mm->brk since arg_lock can't prevent from concurrent writing from sys_brk(). We may use arg_lock to protect everything else other than mm->brk. The complexity sounds acceptable. Of course, as Cyrill mentioned, he prefers to deprecating prctl_set_mm since C/R is the only user of it. We may wait until he is done? Thanks, Yang > > Thanks!