linux-kernel - Re: [PATCH v3] rcu: define tracepoint strings only if CONFIG

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Date:	Mon, 14 Jul 2014 13:03:02 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v3] rcu: define tracepoint strings only if
 CONFIG_TRACING is set

On Sat, 12 Jul 2014 19:01:49 +0200
Ard Biesheuvel <ard.biesheuvel@...aro.org> 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: paulmck@...ux.vnet.ibm.com
> ---
> v3:
> - make definition of <var>_varname conditional as well
> v2:
> - s/DEFINE_TPS/DEFINE_RCU_TPS/
> 
>  kernel/rcu/tree.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 

Reviewed-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index f1ba77363fbb..0756a4696007 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -79,9 +79,18 @@ 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.
>   */
> -#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
> +#ifdef CONFIG_TRACING
> +# define DEFINE_RCU_TPS(sname) \
>  static char sname##_varname[] = #sname; \
> -static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
> +static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
> +# define RCU_STATE_NAME(sname) sname##_varname
> +#else
> +# define DEFINE_RCU_TPS(sname)
> +# define RCU_STATE_NAME(sname) __stringify(sname)
> +#endif
> +
> +#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
> +DEFINE_RCU_TPS(sname) \
>  struct rcu_state sname##_state = { \
>  	.level = { &sname##_state.node[0] }, \
>  	.call = cr, \
> @@ -93,7 +102,7 @@ struct rcu_state sname##_state = { \
>  	.orphan_donetail = &sname##_state.orphan_donelist, \
>  	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
>  	.onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
> -	.name = sname##_varname, \
> +	.name = RCU_STATE_NAME(sname), \
>  	.abbr = sabbr, \
>  }; \
>  DEFINE_PER_CPU(struct rcu_data, sname##_data)

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