linux-kernel - Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing update_rq

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Message-ID: <alpine.DEB.2.20.1609212131280.5532@nanos>
Date:   Wed, 21 Sep 2016 21:46:34 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Matt Fleming <matt@...eblueprint.co.uk>
cc:     Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Byungchul Park <byungchul.park@....com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Luca Abeni <luca.abeni@...tn.it>,
        Rik van Riel <riel@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Yuyang Du <yuyang.du@...el.com>, Jan Kara <jack@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Galbraith <umgwanakikbuti@...il.com>
Subject: Re: [PATCH v2 7/7] sched/core: Add debug code to catch missing
 update_rq_clock()

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