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 S1756197AbcIUTtc (ORCPT <rfc822;w@1wt.eu>);
        Wed, 21 Sep 2016 15:49:32 -0400
Received: from Galois.linutronix.de ([146.0.238.70]:35861 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1755570AbcIUTta (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 21 Sep 2016 15:49:30 -0400
Date: Wed, 21 Sep 2016 21:46:34 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Matt Fleming <matt@codeblueprint.co.uk>
cc: Petr Mladek <pmladek@suse.com>, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Byungchul Park <byungchul.park@lge.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Luca Abeni <luca.abeni@unitn.it>, Rik van Riel <riel@redhat.com>,
        Wanpeng Li <wanpeng.li@hotmail.com>, Yuyang Du <yuyang.du@intel.com>,
        Jan Kara <jack@suse.cz>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        linux-kernel@vger.kernel.org, Mel Gorman <mgorman@techsingularity.net>,
        Mike Galbraith <umgwanakikbuti@gmail.com>
Subject: Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing
 update_rq_clock()
In-Reply-To: <20160921190856.GP2892@codeblueprint.co.uk>
Message-ID: <alpine.DEB.2.20.1609212131280.5532@nanos>
References: <20160921133813.31976-1-matt@codeblueprint.co.uk> <20160921133813.31976-8-matt@codeblueprint.co.uk> <20160921155826.GB8408@pathway.suse.cz> <20160921190856.GP2892@codeblueprint.co.uk>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 21 Sep 2016, Matt Fleming wrote:

> On Wed, 21 Sep, at 05:58:27PM, Petr Mladek wrote:
> > 
> > I am not sure how the above call chain is realistic. But adding
> > WARN_ON() into the scheduler paths is risky in general.
> 
> It's not clear to me why this should be the case. WARN_ON() calls have
> existed in the scheduler paths since forever.

Everything which end up in printk within a rq->lock held section has been
have been prone to deadlocks for a very long time. Guess why
printk_deferred (the former printk_sched) exists.

Thanks,

	tglx