linux-kernel - Re: [RFC][PATCH 08/18 v2] ftrace/rcu: Do not trace debug_lockdep_rcu

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Date:	Sat, 31 Aug 2013 12:21:01 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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 08/18 v2] ftrace/rcu: Do not trace
 debug_lockdep_rcu_enabled()

On Sat, Aug 31, 2013 at 01:11:25AM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> 
> The function debug_lockdep_rcu_enabled() is part of the RCU lockdep
> debugging, and is called very frequently. I found that if I enable
> a lot of debugging and run the function graph tracer, this
> function can cause a live lock of the system.
> 
> We don't usually trace lockdep infrastructure, no need to trace
> this either.
> 
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Or I can just take it, if you would rather.  (If so, 3.12 or 3.13?)

> ---
>  kernel/rcupdate.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
> index cce6ba8..4f20c6c 100644
> --- a/kernel/rcupdate.c
> +++ b/kernel/rcupdate.c
> @@ -122,7 +122,7 @@ struct lockdep_map rcu_sched_lock_map =
>  	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
>  EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
> 
> -int debug_lockdep_rcu_enabled(void)
> +int notrace debug_lockdep_rcu_enabled(void)
>  {
>  	return rcu_scheduler_active && debug_locks &&
>  	       current->lockdep_recursion == 0;
> -- 
> 1.7.10.4
> 
> 

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