linux-kernel - Re: [PATCH] rcu: define tracepoint strings only if CONFIG

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Message-ID: <CAKv+Gu-2Tgf+gvh=LPWFpkgFAVb8qe0Gdp2Va5Br19BwLzK9yw@mail.gmail.com>
Date:	Fri, 11 Jul 2014 17:40:33 +0200
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	paulmck <paulmck@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dipankar <dipankar@...ibm.com>
Subject: Re: [PATCH] rcu: define tracepoint strings only if CONFIG_TRACING is set

On 11 July 2014 17:30, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Fri, 11 Jul 2014 08:12:40 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
>
>> On Fri, Jul 11, 2014 at 01:38:12PM +0200, Ard Biesheuvel wrote:
>> > Commit f7f7bac9cb1c ("rcu: Have the RCU tracepoints use the tracepoint_string
>> > infrastructure") unconditionally populates the __tracepoint_str input section,
>> > but this section is not assigned an output section if CONFIG_TRACING is not set.
>> > This results in the __tracepoint_str turning up in unexpected places, i.e.,
>> > after _edata.
>> >
>> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> > Cc: rostedt@...dmis.org
>> > Cc: dipankar@...ibm.com
>> > Cc: paulmck@...ux.vnet.ibm.com
>>
>> If you get a Reviewed-by from Steven Rostedt, I will be happy to queue
>> this one.
>
> I'm fine with it, but it should add a comment.
>
>
>>
>>                                                       Thanx, Paul
>>
>> > ---
>> >  kernel/rcu/tree.c | 9 ++++++++-
>> >  1 file changed, 8 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> > index f1ba77363fbb..ac1984149eb5 100644
>> > --- a/kernel/rcu/tree.c
>> > +++ b/kernel/rcu/tree.c
>> > @@ -79,9 +79,16 @@ static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
>> >   * the tracing userspace tools to be able to decipher the string
>> >   * address to the matching string.
>> >   */
>> > +#ifdef CONFIG_TRACING
>
> /*
>  * When tracing is enabled, DEFINE_TPS() will export the string to
>  * userspace via the tracing debugfs directory. This allows userspace
>  * tools to read the binary tracepoints that reference the pointer
>  * to the string and not the string itself.
>  */
>
>
>> > +#define DEFINE_TPS(sname) \
>> > +static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
>> > +#else
>> > +#define DEFINE_TPS(sname)
>> > +#endif
>
> Also, perhaps we should call it:
>
>  DEFINE_RCU_TPS()
>
> Other than that, I'm fine with the patch.
>
> I'll review v2 ;-)
>

Thanks gents, v2 coming up.

-- 
Ard.


>> > +
>> >  #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
>> >  static char sname##_varname[] = #sname; \
>> > -static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
>> > +DEFINE_TPS(sname) \
>> >  struct rcu_state sname##_state = { \
>> >     .level = { &sname##_state.node[0] }, \
>> >     .call = cr, \
>> > --
>> > 1.8.3.2
>> >
>
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