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

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Message-ID: <20180507214611.GB13787@joelaf.mtv.corp.google.com>
Date:   Mon, 7 May 2018 14:46:11 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
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 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.

thanks,

- Joel