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[195.135.220.15]) by mx.google.com with ESMTPS id gu5si2876913ejb.282.2019.04.17.06.41.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Apr 2019 06:41:54 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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