linux-kernel - Re: [PATCH v2 9/9] perf,tracing: Allow function tracing when !RCU

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Date:   Fri, 14 Feb 2020 17:48:45 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com
Subject: Re: [PATCH v2 9/9] perf,tracing: Allow function tracing when !RCU

On Fri, 14 Feb 2020 14:38:14 -0600
Kim Phillips <kim.phillips@....com> wrote:

> On 2/12/20 3:01 PM, Peter Zijlstra wrote:
> > Since perf is now able to deal with !rcu_is_watching() contexts,
> > remove the restraint.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > ---
> >  kernel/trace/trace_event_perf.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- a/kernel/trace/trace_event_perf.c
> > +++ b/kernel/trace/trace_event_perf.c
> > @@ -477,7 +477,7 @@ static int perf_ftrace_function_register
> >  {
> >  	struct ftrace_ops *ops = &event->ftrace_ops;
> >  
> > -	ops->flags   = FTRACE_OPS_FL_RCU;
> > +	ops->flags   = 0;
> >  	ops->func    = perf_ftrace_function_call;
> >  	ops->private = (void *)(unsigned long)nr_cpu_ids;  
> 
> If this is the last user of the flag, should all remaining
> FTRACE_OPS_FL_RCU references be removed, too?

Let's wait till Peter's patches goes through a merge cycle or two. I
want to make sure there's no other RCU issues that pop up before we
remove this infrastructure.

-- Steve