linux-kernel - Re: [patch 1/3] rtmutex: Add missing deadlock check

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Message-ID: <alpine.DEB.2.02.1405140845330.6261@ionos.tec.linutronix.de>
Date:	Wed, 14 May 2014 08:54:40 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	paulmck@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Darren Hart <darren@...art.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Ingo Molnar <mingo@...nel.org>,
	Clark Williams <williams@...hat.com>,
	Roland McGrath <roland@...k.frob.com>,
	Carlos ODonell <carlos@...hat.com>,
	Jakub Jelinek <jakub@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [patch 1/3] rtmutex: Add missing deadlock check



On Tue, 13 May 2014, Steven Rostedt wrote:

> On Tue, 13 May 2014 16:27:11 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > On Tue, May 13, 2014 at 06:44:30PM -0400, Steven Rostedt wrote:
> > > On Tue, 13 May 2014 15:00:09 -0700
> > > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > > 
> > > 
> > > > Good points -- I was indeed thinking about stress testing instead of
> > > > algorithmic testing.
> > > 
> > > But doesn't lockdep use algorithmic tests too?
> > 
> > I suppose you could argue that there is no such thing as non-algorithmic
> > testing, given that all test code uses an algorithm of some sort.  Perhaps
> > with the exception of letting your pet walk across the keyboard.  ;-)
> > 
> > Perhaps I should have instead said that I was thinking about random
> > testing instead of formal testing?
> 
> Actually it still applies, but I was mistaken, it's not lockdep itself,
> it's the LOCKING_API_SELFTESTS. They are a form of formal testing as
> suppose to random testing.
> 
> See lib/locking-selftest.c.
> 
> That looks more like something we can do for the rtmutex code, or even
> add to it.

It's called from very early init. So no threads ...

Thinking about it with a bit more awake brain, we probably can do it
completely from user space via futex except for a single case, which
we handle in the futex code: recursive AA of a single task.

I want to look into ABBA et al detection for the futexes anyway, so
that might be sufficient. Need to do a few experiments.

Thanks,

	tglx


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