linux-kernel - Re: [RFC][PATCH] preempt: Debug for possible missed preemption checks

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Message-ID: <20140117090856.GE11314@laptop.programming.kicks-ass.net>
Date:	Fri, 17 Jan 2014 10:08:56 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <williams@...hat.com>
Subject: Re: [RFC][PATCH] preempt: Debug for possible missed preemption checks

On Thu, Jan 16, 2014 at 09:12:14PM -0800, Andrew Morton wrote:
> On Thu, 16 Jan 2014 23:57:51 -0500 Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > When PROVE_LOCKING and PREEMPT is configured, the preempt state
> > tracking is active. Testing this out, I added a module that did the
> > following:
> 
> So I assume your kernel at least has no instances of this bug, so we
> don't need the patch ;) It *is* a fairly daft thing to do.

Yeah, its exceedingly daft, but I do run into it every so often. Say
once a year or so.

Also, its usually not really a problem on 'normal' kernels, but it
absolutely blows on -rt.
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