linux-kernel - Re: [PATCH] kernel/pid.c: check pid whether be NULL in __change

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Message-ID: <20131007124319.GA24450@redhat.com>
Date:	Mon, 7 Oct 2013 14:43:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/pid.c: check pid whether be NULL in
	__change_pid()

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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