linux-kernel - Re: [RFC][PATCH] tracing: Have stack tracer force RCU to be watching

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Message-ID: <20151021073922.77e429f6@gandalf.local.home>
Date:	Wed, 21 Oct 2015 07:39:22 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] tracing: Have stack tracer force RCU to be
 watching

On Wed, 21 Oct 2015 10:01:42 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> > I should probably add a "if (in_nmi()) return" somewhere.
> 
> But if there's an arch that doesn't use a separate NMI stack, the NMI
> might cause the largest stack, which would then remain invisible from
> the stack-tracer.
> 
> Should we not instead fix the NMI-safety of this tracer?

We could, but that should be a separate project, as that would require
doing everything lockless, which would require a redesign. Is that
worth it?

For now, the safe thing to do is the if (in_nmi()), but certainly, if
someone gets time to make it NMI safe, we can do that too.

-- Steve
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