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

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Date:	Fri, 11 Jul 2014 20:09:26 +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 17:40, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
> 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.
>>  */
>>
>>

Ehm, actually, a comment to that effect is already right there in the file.
Would you still like me to add this additional comment?

>>> > +#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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