Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 27 Apr 2018 09:30:05 -0700
Joel Fernandes <joelaf@google.com> wrote:

> On Fri, Apr 27, 2018 at 7:47 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Fri, 27 Apr 2018 10:26:29 -0400 (EDT)
> > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> >  
> >> The general approach and the implementation look fine, except for
> >> one small detail: I would be tempted to explicitly disable preemption
> >> around the call to the tracepoint callback for the rcuidle variant,
> >> unless we plan to audit every tracer right away to remove any assumption
> >> that preemption is disabled in the callback implementation.  
> >
> > I'm thinking that we do that audit. There shouldn't be many instances
> > of it. I like the idea that a tracepoint callback gets called with
> > preemption enabled.  
> 
> Here is the list of all callers of the _rcuidle :

I was thinking of auditing who registers callbacks to any tracepoints.

-- Steve

> 
> trace_clk_disable_complete_rcuidle
> trace_clk_disable_rcuidle
> trace_clk_enable_complete_rcuidle
> trace_clk_enable_rcuidle
> trace_console_rcuidle
> trace_cpu_idle_rcuidle
> trace_ipi_entry_rcuidle
> trace_ipi_exit_rcuidle
> trace_ipi_raise_rcuidle
> trace_irq_disable_rcuidle
> trace_irq_enable_rcuidle
> trace_power_domain_target_rcuidle
> trace_preempt_disable_rcuidle
> trace_preempt_enable_rcuidle
> trace_rpm_idle_rcuidle
> trace_rpm_resume_rcuidle
> trace_rpm_return_int_rcuidle
> trace_rpm_suspend_rcuidle
> trace_tlb_flush_rcuidle
> 
> All of these are either called from irqs or preemption disabled
> already. So I think it should be fine to keep preemption on. But I'm
> Ok with disabling it before callback execution if we agree that we
> want that.
> 
> (and the ring buffer code is able to cope anyway Steven pointed).
> 
> thanks,
> 
>  - Joel