Date: Mon, 7 Oct 2013 14:43:19 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Chen Gang <gang.chen@asianux.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kernel/pid.c: check pid whether be NULL in
	__change_pid()
Message-ID: <20131007124319.GA24450@redhat.com>
References: <52528CF7.8050405@asianux.com>
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On 10/07, Chen Gang wrote:
>
> Within __change_pid(), 'new' may be NULL if it comes from detach_pid(),
> and 'link->pid' also may be NULL ("link->pid = new"), so theoretically,\
> the original 'link->pid' may be NULL, too.

I don't really understand this "theoretically",

> In real world, at least now, all callers which will call detach_pid()
> or change_pid() will not cause issue,

Yes,

> but still recommend to check it
> in __change_pid() to let itself consistency.

Why?

Contrary, I think we should not hide the problem. If __change_pid() is
called when task->pids[type].pid is already NULL there is something
seriously wrong.

Oleg.

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