From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754163Ab0BHRRh (ORCPT <rfc822;w@1wt.eu>);
	Mon, 8 Feb 2010 12:17:37 -0500
Received: from mx1.redhat.com ([209.132.183.28]:60210 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1753791Ab0BHRRg (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 8 Feb 2010 12:17:36 -0500
Date: Mon, 8 Feb 2010 18:16:44 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
       linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com,
       linux-security-module@vger.kernel.org
Subject: Re: [PATCH] Update comment on find_task_by_pid_ns
Message-ID: <20100208171643.GA19230@redhat.com>
References: <20091210001308.247025548@linutronix.de> <20091210004703.029784964@linutronix.de> <20091210142036.GA8226@redhat.com> <200912110008.BEJ00511.FVOJLtSMOFHOQF@I-love.SAKURA.ne.jp> <alpine.LFD.2.00.0912102214180.3089@localhost.localdomain> <201002082130.JDC57339.OHOVJFQtFSLFMO@I-love.SAKURA.ne.jp> <20100208132101.GA7129@redhat.com> <alpine.LFD.2.00.1002081802510.2811@localhost.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <alpine.LFD.2.00.1002081802510.2811@localhost.localdomain>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 02/08, Thomas Gleixner wrote:
>
> On Mon, 8 Feb 2010, Oleg Nesterov wrote:
>
> > IOW, if we change copy_process()
> >
> > 	--- kernel/fork.c
> > 	+++ kernel/fork.c
> > 	@@ -1304,8 +1304,11 @@ static struct task_struct *copy_process(
> > 		return p;
> >
> > 	 bad_fork_free_pid:
> > 	-	if (pid != &init_struct_pid)
> > 	+	if (pid != &init_struct_pid) {
> > 	+		read_lock(&tasklist_lock);
> > 			free_pid(pid);
> > 	+		read_unlock(&tasklist_lock);
> > 	+	}
> > 	 bad_fork_cleanup_io:
> > 		if (p->io_context)
> > 			exit_io_context(p);
> >
> > then find_task_by_pid_ns/etc could be used under tasklist safely even
> > with PREEMPT_RCU.
>
> We try to get rid of the read_lock sites of tasklist_lock, so please
> let's not think about adding more :)

Yes, yes, I agree. I didn't mean this patch makes sense.

Oleg.