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Date: Sat, 23 Aug 2014 15:30:01 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Kees Cook <keescook@chromium.org>, Tejun Heo <tj@kernel.org>,
        Andrew Vagin <avagin@openvz.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
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        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Julien Tinnes <jln@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: + prctl-pr_set_mm-introduce-pr_set_mm_map-operation-v3.patch
	added to -mm tree
Message-ID: <20140823133001.GA966@redhat.com>
References: <20140822192241.GA26512@redhat.com> <20140822201550.GA25918@moon> <20140823115302.GA27587@redhat.com> <20140823122214.GF25918@moon> <20140823131412.GA31685@redhat.com>
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forgot to mention,

On 08/23, Oleg Nesterov wrote:
>
> On 08/23, Cyrill Gorcunov wrote:
>
> > Looks like I need
> > to use cred_guard_mutex instead of task_lock here, no?
>
> Please don't. First of all, it can't help because proc_pid_auxv() doesn't hold
> this lock. It does mm_access() which drops this lock after return. And to remind,
> we are going to remove mm_access/lock_trace from sys_read() paths in proc.

Besides, it can't help anyway. cred_guard_mutex is per-process (not per-thread),
suppose that a vfork()'ed child does prctl() while another thread reads the
parent's /proc/pid/auxv.

Cyrill, I am sorry, but I am starting to think that this patch should be
dropped and replaced by another version. Or do you think it would be better
to send the fixes on top?

Oleg.