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From:   Joel Fernandes <joelaf@google.com>
Date:   Fri, 27 Apr 2018 11:11:47 -0700
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Subject: Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing
 with preempt on
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
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        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Boqun Feng <boqun.feng@gmail.com>,
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        fweisbec <fweisbec@gmail.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        kbuild test robot <fengguang.wu@intel.com>,
        baohong liu <baohong.liu@intel.com>,
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        "Cc: Android Kernel" <kernel-team@android.com>
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On Fri, Apr 27, 2018 at 9:37 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> 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.

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