linux-kernel - Re: [PATCH] tracing: generate RCU warnings even when tracepoints are disabled

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Date:	Fri, 8 Aug 2014 14:30:22 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org,
	dave.hansen@...ux.intel.com, davej@...hat.com, mingo@...hat.com
Subject: Re: [PATCH] tracing: generate RCU warnings even when tracepoints
 are disabled

On Thu, 7 Aug 2014 11:13:56 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> On Thu, Aug 07, 2014 at 10:52:04AM -0700, Dave Hansen wrote:
> > 
> > From: Dave Hansen <dave.hansen@...ux.intel.com>
> > 
> > Dave Jones reported seeing a bug from one of my TLB tracepoints:
> > 
> > 	http://lkml.kernel.org/r/20140806181801.GA4605@redhat.com
> > 
> > I've been running these patches for months and never saw this.
> > But, a big chunk of my testing, especially with all the debugging
> > enabled, was in a vm where intel_idle doesn't work.  On the
> > systems where I was using intel_idle, I never had lockdep enabled
> > and this tracepoint on at the same time.
> > 
> > This patch ensures that whenever we have lockdep available, we do
> > _some_ RCU activity at the site of the tracepoint, despite
> > whether the tracepoint's condition matches or even if the
> > tracepoint itself is completely disabled.  This is a bit of a
> > hack, but it is pretty self-contained.
> > 
> > I confirmed that with this patch plus lockdep I get the same
> > splat as Dave Jones did, but without enabling the tracepoint
> > explicitly.
> > 
> > Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> > Cc: Dave Jones <davej@...hat.com>,
> > Cc: paulmck@...ux.vnet.ibm.com
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> 
> Looks good to me, but I must defer to Steven on this one.
> 

Looks fine. I can add it to my 3.18 queue.

Paul, want to send me an "Acked-by"?

Thanks,

-- Steve

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