linux-kernel - Re: [PATCH v2] tracing/perf: Move rcu_irq_enter/exit

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Date:   Wed, 12 Feb 2020 01:05:20 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH v2] tracing/perf: Move rcu_irq_enter/exit_irqson() to
 perf trace point hook

On Wed, Feb 12, 2020 at 09:05:22AM +0100, Peter Zijlstra wrote:
> On Tue, Feb 11, 2020 at 10:54:57AM -0800, Paul E. McKenney wrote:
> > On Tue, Feb 11, 2020 at 06:32:13PM +0100, Peter Zijlstra wrote:
> > > On Tue, Feb 11, 2020 at 06:29:52PM +0100, Peter Zijlstra wrote:
> > > > +#define trace_rcu_enter()					\
> > > > +({								\
> > > > +	unsigned long state = 0;				\
> > > > +	if (!rcu_is_watching())	{				\
> > > 
> > > Also, afaict rcu_is_watching() itself needs more love, the functio has
> > > notrace, but calls other stuff that does not have notrace or inline.
> > 
> > Good catch!  Like this?
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 1f5fdf7..51616e72 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -295,7 +295,7 @@ static void rcu_dynticks_eqs_online(void)
> >   *
> >   * No ordering, as we are sampling CPU-local information.
> >   */
> > -static bool rcu_dynticks_curr_cpu_in_eqs(void)
> > +static bool notrace rcu_dynticks_curr_cpu_in_eqs(void)
> 
> Right, except that, given the size of the thing, I'd opt for 'inline'
> over 'notrace'.

Like this, then?

							Thanx, Paul

------------------------------------------------------------------------

commit 164a7e5204cf32d22d0e444efd97ac7f2243b8d2
Author: Paul E. McKenney <paulmck@...nel.org>
Date:   Tue Feb 11 11:10:00 2020 -0800

    rcu: Make rcu_dynticks_curr_cpu_in_eqs() be inline
    
    The rcu_is_watching() function is and must be notrace in order to allow
    it to be used by the tracing infrastructure.  However, it also invokes
    rcu_dynticks_curr_cpu_in_eqs(), which therefore needs to be either
    notrace or inline.  But isn't.
    
    This commit therefore adds "inline" to the rcu_dynticks_curr_cpu_in_eqs()
    definition.
    
    Reported-by: Peter Zijlstra <peterz@...radead.org>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1f5fdf7..16fd113 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -295,7 +295,7 @@ static void rcu_dynticks_eqs_online(void)
  *
  * No ordering, as we are sampling CPU-local information.
  */
-static bool rcu_dynticks_curr_cpu_in_eqs(void)
+static bool inline rcu_dynticks_curr_cpu_in_eqs(void)
 {
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);