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

From: Joel Fernandes <joelaf@google.com>
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>,
	Tom Zanussi <tom.zanussi@linux.intel.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Boqun Feng <boqun.feng@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	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>,
	vedang patel <vedang.patel@intel.com>,
	"Cc: Android Kernel" <kernel-team@android.com>
Subject: Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on
Date: Fri, 27 Apr 2018 11:11:47 -0700	[thread overview]
Message-ID: <CAJWu+ore5pOF9Ld7H2K=Y4JZiRvy8T86MA+dN8-8BTHPCsau1w@mail.gmail.com> (raw)
In-Reply-To: <20180427123759.0bc4b8de@gandalf.local.home>

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