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

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Message-ID: <20180427123759.0bc4b8de@gandalf.local.home>
Date:   Fri, 27 Apr 2018 12:37:59 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        fweisbec <fweisbec@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        kbuild test robot <fengguang.wu@...el.com>,
        baohong liu <baohong.liu@...el.com>,
        vedang patel <vedang.patel@...el.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks
 executing with preempt on

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

> On Fri, Apr 27, 2018 at 7:47 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > On Fri, 27 Apr 2018 10:26:29 -0400 (EDT)
> > Mathieu Desnoyers <mathieu.desnoyers@...icios.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