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 S1752749AbaI3Ntg (ORCPT <rfc822;w@1wt.eu>);
	Tue, 30 Sep 2014 09:49:36 -0400
Received: from casper.infradead.org ([85.118.1.10]:44473 "EHLO
	casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752482AbaI3Ntb (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 30 Sep 2014 09:49:31 -0400
Date: Tue, 30 Sep 2014 15:49:28 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: mingo@kernel.org, torvalds@linux-foundation.org, tglx@linutronix.de,
        ilya.dryomov@inktank.com, umgwanakikbuti@gmail.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 10/11] sched: Debug nested sleeps
Message-ID: <20140930134928.GF4241@worktop.programming.kicks-ass.net>
References: <20140924081845.572814794@infradead.org>
 <20140924082242.591637616@infradead.org>
 <20140929221344.GB12112@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20140929221344.GB12112@redhat.com>
User-Agent: Mutt/1.5.22.1 (2013-10-16)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Sep 30, 2014 at 12:13:44AM +0200, Oleg Nesterov wrote:
> On 09/24, Peter Zijlstra wrote:
> >
> > +#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> > +
> > +#define __set_task_state(tsk, state_value)			\
> > +	do {							\
> > +		(tsk)->task_state_change = _THIS_IP_;		\
> > +		(tsk)->state = (state_value);			\
> > +	} while (0)
> 
> ...
> 
> > @@ -7143,6 +7143,19 @@ void __might_sleep(const char *file, int
> >  {
> >  	static unsigned long prev_jiffy;	/* ratelimiting */
> >
> > +	/*
> > +	 * Blocking primitives will set (and therefore destroy) current->state,
> > +	 * since we will exit with TASK_RUNNING make sure we enter with it,
> > +	 * otherwise we will destroy state.
> > +	 */
> > +	if (WARN(current->state != TASK_RUNNING,
> > +			"do not call blocking ops when !TASK_RUNNING; "
> > +			"state=%lx set at [<%p>] %pS\n",
> > +			current->state,
> > +			(void *)current->task_state_change,
> > +			(void *)current->task_state_change))
> > +		__set_current_state(TASK_RUNNING);
> 
> Question: now that we have ->task_state_change, perhaps it makes sense
> to redefine fixup_sleep()
> 
> 	#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> 	#define fixup_sleep()	(current->task_state_change = 0)
> 	#else
> 	#define fixup_sleep()	do { } while (0)
> 	#endif
> 
> and make the WARN() above depend on task_state_change != 0 ?
> 
> This is minor, but this way CONFIG_DEBUG_ATOMIC_SLEEP will not imply
> a subtle behavioural change.

You mean the __set_current_state() that's extra? I would actually argue
to keep that since it makes the 'problem' much worse.