linux-kernel - Re: [PATCH] ftrace: Remove use of control list and ops

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Date:	Wed, 2 Dec 2015 08:59:11 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] ftrace: Remove use of control list and ops

On Tue, Dec 01, 2015 at 11:56:55AM -0500, Steven Rostedt wrote:
> On Tue, 1 Dec 2015 16:57:44 +0100
> Jiri Olsa <jolsa@...hat.com> wrote:
> 
> 
> > > Hmm, I thought that I forced the list function when RCU or PER_CPU
> > > was set. Oh wait. I have CONFIG_PREEMPT set, which will change the
> > > logic slightly. I'm guessing you have PREEMPT_VOLUNTARY set. I'll try
> > > that out.  
> > 
> > yep, but the trampoline has separate code path
> > to set the ops func
> 
> Right, but that only gets called for DYNAMIC ops (which perf is) when
> CONFIG_PREEMPT is not set. What about this patch instead? (on top of my
> other one)
> 
> It's a lot like yours, but instead of creating a new helper function, I
> just reuse the recurs_func instead.
> 
> -- Steve
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 8b22e681baf8..05ed87d06bb0 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5230,20 +5230,29 @@ static void ftrace_ops_no_ops(unsigned long ip, unsigned long parent_ip)
>  
>  /*
>   * If there's only one function registered but it does not support
> - * recursion, this function will be called by the mcount trampoline.
> - * This function will handle recursion protection.
> + * recursion, needs RCU protection and/or requires per cpu handling, then
> + * this function will be called by the mcount trampoline.
>   */
> -static void ftrace_ops_recurs_func(unsigned long ip, unsigned long parent_ip,
> +static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip,
>  				   struct ftrace_ops *op, struct pt_regs *regs)
>  {
>  	int bit;
>  
> +	if ((op->flags & FTRACE_OPS_FL_RCU) && !rcu_is_watching())
> +		return;
> +
>  	bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX);
>  	if (bit < 0)
>  		return;
>  
> -	op->func(ip, parent_ip, op, regs);
> +	preempt_disable_notrace();

I was wondering about not disabling preemption in the original
ftrace_ops_recurs_func function.. thats why I added new one ;-)

I'll test the patch

thanks,
jirka

>  
> +	if (!(op->flags & FTRACE_OPS_FL_PER_CPU) ||
> +	    ftrace_function_local_disabled(op)) {
> +		op->func(ip, parent_ip, op, regs);
> +	}
> +
> +	preempt_enable_notrace();
>  	trace_clear_recursion(bit);
--
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