linux-kernel - Re: [RFC][PATCH 11/18 v2] ftrace: Adde infrastructure to stop RCU unsafe checker from checking

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Date:	Sat, 31 Aug 2013 16:40:04 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [RFC][PATCH 11/18 v2] ftrace: Adde infrastructure to stop RCU
 unsafe checker from checking

On Sat, 2013-08-31 at 12:52 -0700, Paul E. McKenney wrote:
> On Sat, Aug 31, 2013 at 01:11:28AM -0400, Steven Rostedt wrote:
> > From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> > 
> > This is a light weight way to keep the rcu checker from checking
> > RCU safety. It adds a ftrace_unsafe_rcu_checker_disable/enable()
> > that increments or decrements a counter respectively. When the
> > counter is set, the RCU unsafe checker callback does not run the
> > tests to see if RCU is safe or not.
> 
> Please add something saying what we do instead of testing RCU safety.
> Looks to me like it skips not only the tests, but also invoking the
> callback, but I could easily be wrong.

Yeah, the change log sucks. I wrote the change logs after 1am and was
half asleep. I see I wrote "Add" as "Adde" ;-)

> 
> > This is required by the graph tracer because the checks can cause
> > the graph tracer to live lock the system by its own calls.
> > 
> > It's also needed by the irqsoff tracer, because it may be called
> > in RCU unsafe regions and if its internal functions get traced
> > then the RCU unsafe checker may have some false positives.
> > 
> > Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> 
> With the augmented commit log as noted above:
> 
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 

Thanks, come Tuesday, I'll update the logs.

-- Steve

> > ---
> >  kernel/trace/trace.h           |   12 +++++++++---
> >  kernel/trace/trace_functions.c |   15 +++++++++++++++
> >  2 files changed, 24 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > index e551316..58e4c37 100644
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -760,9 +760,6 @@ static inline int ftrace_graph_addr(unsigned long addr)


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