linux-kernel - Re: [PATCH] move tty_kref_put() outside of __cleanup

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Message-ID: <20100318225102.6a5578d9@lxorguk.ukuu.org.uk>
Date:	Thu, 18 Mar 2010 22:51:02 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...ux.intel.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] move tty_kref_put() outside of __cleanup_signal()

> -			tty_kref_put(p->signal->tty);
>  			p->signal->tty = tty_kref_get(current->signal->tty);

That bit needs commenting clearly or a WARN_ON() that p->signal->tty is
NULL before the get otherwise when the assumption is broken the flaw will
be subtle and hard to find.

>  			attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
>  			attach_pid(p, PIDTYPE_SID, task_session(current));
> --- 34-rc1/kernel/exit.c~7_TTY_PUT	2010-03-17 20:05:38.000000000 +0100
> +++ 34-rc1/kernel/exit.c	2010-03-18 22:46:41.000000000 +0100
> @@ -150,6 +150,7 @@ static void __exit_signal(struct task_st
>  		 * see account_group_exec_runtime().
>  		 */
>  		task_rq_unlock_wait(tsk);
> +		tty_kref_put(sig->tty);

and a sig->tty = NULL assignment to trap races might not go amiss here
perhaps ?


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