linux-kernel - Re: [PATCH RFC v6 4/5] tracepoint: Make rcuidle tracepoint callers use SRCU

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Date:   Mon, 7 May 2018 20:37:54 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     "Joel Fernandes, Google" <joel@...lfernandes.org>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        rostedt <rostedt@...dmis.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>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH RFC v6 4/5] tracepoint: Make rcuidle tracepoint callers
 use SRCU

----- On May 7, 2018, at 5:46 PM, Joel Fernandes, Google joel@...lfernandes.org wrote:

> On Mon, May 07, 2018 at 05:05:41PM -0400, Mathieu Desnoyers wrote:
>> ----- On May 7, 2018, at 4:41 PM, Joel Fernandes joelaf@...gle.com wrote:
>> [...]
>> > +extern struct srcu_struct tracepoint_srcu;
>> > +
>> > extern int
>> > tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);
>> > extern int
>> > @@ -77,6 +80,9 @@ int unregister_tracepoint_module_notifier(struct
>> > notifier_block *nb)
>> >  */
>> > static inline void tracepoint_synchronize_unregister(void)
>> > {
>> > +#ifdef CONFIG_TRACEPOINTS
>> > +	synchronize_srcu(&tracepoint_srcu);
>> > +#endif
>> > 	synchronize_sched();
>> 
>> Why is this ifdef needed ?
> 
> tracepoint_srcu is defined in tracepoint.c so if we don't protect usage here, it
> would cause a build error.

Then we should ifdef the entire implementation of tracepoint_synchronize_unregister().
There is no point in issuing synchronize_sched() when code invokes that
function on a CONFIG_TRACEPOINTS=n config.

Thanks,

Mathieu


> 
> thanks,
> 
> - Joel

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com