linux-kernel - Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection

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Message-ID: <alpine.DEB.2.00.0904161411320.20429@gandalf.stny.rr.com>
Date:	Thu, 16 Apr 2009 14:12:33 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within
 recursive protection


On Thu, 16 Apr 2009, Peter Zijlstra wrote:
> 
> > That is, at thread context, you are at level 0, if an interrupt comes
> > in, it sets you to level 1, if another interrupt comes in, it sets you to 
> > level 2, and so on.
> > 
> > I guess we could add this into the irq_enter/exit sofirq_enter/exit and 
> > nmi_enter/exit.
> > 
> > Thus we can have each task with a bitmask. When we start to trace, we set 
> > the bit coresponding to the level the task is at.
> > 
> > Ie. in thread context, we set bit 0, if we are interrupted by a 
> > softirq/irq/nmi, we set the level bit we are at. Hmm, we might be able to 
> > do this via the preempt count already :-/
> > 
> > Just add the softirq/irq/nmi bits together.
> > 
> > The if the bit is already set we can dump out a warning.
> > 
> > I'll try that out.
> 
> static int *perf_swcounter_recursion_context(struct perf_cpu_context *cpuctx)
> {
>         if (in_nmi())
>                 return &cpuctx->recursion[3];
> 
>         if (in_irq())
>                 return &cpuctx->recursion[2];
> 
>         if (in_softirq())
>                 return &cpuctx->recursion[1];
> 
>         return &cpuctx->recursion[0];
> }
> 
> Is what I use for perf-counters.

But does that allow multi nested interrupts?

I'll try the preempt_count and let you know.

Thanks,

-- Steve

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