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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 6D42AC282DA for ; Wed, 17 Apr 2019 13:41:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3AE7221773 for ; Wed, 17 Apr 2019 13:41:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555508516; bh=c6VDO5ZevrMLWD0rc/Hyyfd69c30AayWYCM0yESRcAQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=K/WpVgXmFyqGRdLLwl5wtAqaPaFyOrRx3WZ5Rzia3VunmX4UOyPhdkLAmYDMIGKnQ FPpm9qIsjUp7l+ed8CEpKXTWhzh7sBDJEcMTz0La7vUgTk+HMSuLT3qezwDWPI8UHE 5eu0eQwl+jwxzghLhn2K6WWSzT6ZM3ET7XS3R7Kg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732255AbfDQNlz (ORCPT ); Wed, 17 Apr 2019 09:41:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:35524 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729939AbfDQNly (ORCPT ); Wed, 17 Apr 2019 09:41:54 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 8A131B175; Wed, 17 Apr 2019 13:41:53 +0000 (UTC) Date: Wed, 17 Apr 2019 15:41:52 +0200 From: Michal Hocko To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: Andrew Morton , Mateusz Guzik , Mike Rapoport , Vlastimil Babka , Geert Uytterhoeven , Arun KS , Bartosz Golaszewski , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: get_cmdline use arg_lock instead of mmap_sem Message-ID: <20190417134152.GM5878@dhcp22.suse.cz> References: <20190417120347.15397-1-mkoutny@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190417120347.15397-1-mkoutny@suse.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 17-04-19 14:03:47, Michal Koutny 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. Don't we need to use the lock in prctl_set_mm as well then? > Signed-off-by: Michal Koutný > --- > mm/util.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/util.c b/mm/util.c > index d559bde497a9..568575cceefc 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; > > -- > 2.16.4 -- Michal Hocko SUSE Labs