From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751178AbeC0Si2 (ORCPT ); Tue, 27 Mar 2018 14:38:28 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:47870 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750926AbeC0Si0 (ORCPT ); Tue, 27 Mar 2018 14:38:26 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04446;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0T-Btkg2_1522175895; Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct 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 References: <1522088439-105930-1-git-send-email-yang.shi@linux.alibaba.com> <20180327062939.GV5652@dhcp22.suse.cz> From: Yang Shi Message-ID: <95a107ac-5e5b-92d7-dbde-2e961d85de28@linux.alibaba.com> Date: Tue, 27 Mar 2018 14:38:11 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 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: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/27/18 2:29 AM, 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. Yes, sure. > > 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. Actually, I didn't think of why. It looks prctl_set_mm() checks if vma does exist when it tries to set stack_start, argv_* and env_*, btw not only env_end. Cyrill may be able to give us some hint since C/R is the main user of this API. Yang > > Thanks!