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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=unavailable 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 28C6BC04AA6 for ; Tue, 30 Apr 2019 09:10:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EAE5920652 for ; Tue, 30 Apr 2019 09:10:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726846AbfD3JKH (ORCPT ); Tue, 30 Apr 2019 05:10:07 -0400 Received: from relay.sw.ru ([185.231.240.75]:38976 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726165AbfD3JKH (ORCPT ); Tue, 30 Apr 2019 05:10:07 -0400 Received: from [172.16.25.169] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1hLOlz-0007UE-CV; Tue, 30 Apr 2019 12:09:59 +0300 Subject: Re: [PATCH 1/3] mm: get_cmdline use arg_lock instead of mmap_sem To: =?UTF-8?Q?Michal_Koutn=c3=bd?= , gorcunov@gmail.com Cc: akpm@linux-foundation.org, arunks@codeaurora.org, brgl@bgdev.pl, geert+renesas@glider.be, ldufour@linux.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mguzik@redhat.com, mhocko@kernel.org, rppt@linux.ibm.com, vbabka@suse.cz References: <20190418182321.GJ3040@uranus.lan> <20190430081844.22597-1-mkoutny@suse.com> <20190430081844.22597-2-mkoutny@suse.com> From: Kirill Tkhai Message-ID: <4c79fb09-c310-4426-68f7-8b268100359a@virtuozzo.com> Date: Tue, 30 Apr 2019 12:09:57 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190430081844.22597-2-mkoutny@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.04.2019 11:18, Michal Koutný wrote: > The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap > semaphore taken.") added synchronization of reading argument/environment > boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce > arg_lock to protect arg_start|end and env_start|end in mm_struct") > avoided the coarse use of mmap_sem in similar situations. > > get_cmdline can also use arg_lock instead of mmap_sem when it reads the > boundaries. > > Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") > Cc: Yang Shi > Cc: Mateusz Guzik > Signed-off-by: Michal Koutný > Signed-off-by: Laurent Dufour > --- > mm/util.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/util.c b/mm/util.c > index 43a2984bccaa..5cf0e84a0823 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen) > if (!mm->arg_end) > goto out_mm; /* Shh! No looking before we're done */ > > - down_read(&mm->mmap_sem); > + spin_lock(&mm->arg_lock); > arg_start = mm->arg_start; > arg_end = mm->arg_end; > env_start = mm->env_start; > env_end = mm->env_end; > - up_read(&mm->mmap_sem); > + spin_unlock(&mm->arg_lock); > > len = arg_end - arg_start; This looks OK for me. But speaking about existing code it's a secret for me, why we ignore arg_lock in binfmt code, e.g. in load_elf_binary().