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

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Date:   Fri, 27 Apr 2018 11:11:47 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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, Apr 27, 2018 at 9:37 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 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.

Ok. If you feel strongly about this, I think for now I could also just
wrap the callback execution with preempt_disable_notrace. And, when/if
we get to doing the blocking callbacks work, we can considering
keeping preempts on.

thanks,

- Joel