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

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Message-ID: <121a6b11-2fe1-6d9b-2861-a8ef8b42c452@amd.com>
Date:   Fri, 14 Feb 2020 14:38:14 -0600
From:   Kim Phillips <kim.phillips@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        rostedt@...dmis.org
Cc:     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 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?

Thanks,

Kim