linux-kernel - Re: [PATCH rcu 01/20] rcu-tasks: Fix warning for unused tasks_rcu_exit

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Message-ID: <ZCbK7hcVWFEFcPwN@lothringen>
Date:   Fri, 31 Mar 2023 13:58:38 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...a.com, rostedt@...dmis.org, hch@....de,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH rcu 01/20] rcu-tasks: Fix warning for unused
 tasks_rcu_exit_srcu

On Thu, Mar 30, 2023 at 03:47:07PM -0700, Paul E. McKenney wrote:
> The tasks_rcu_exit_srcu variable is used only by kernels built
> with CONFIG_TASKS_RCU=y, but is defined for all kernesl with
> CONFIG_TASKS_RCU_GENERIC=y.  Therefore, in kernels built with
> CONFIG_TASKS_RCU_GENERIC=y but CONFIG_TASKS_RCU=n, this gives
> a "defined but not used" warning.
> 
> This commit therefore moves this variable under CONFIG_TASKS_RCU.
> 
> Link: https://lore.kernel.org/oe-kbuild-all/202303191536.XzMSyzTl-lkp@intel.com/
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  kernel/rcu/tasks.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index bfb5e1549f2b..185358c2f08d 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -136,8 +136,10 @@ static struct rcu_tasks rt_name =							\
>  	.kname = #rt_name,								\
>  }
>  
> +#ifdef CONFIG_TASKS_RCU
>  /* Track exiting tasks in order to allow them to be waited for. */
>  DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
> +#endif

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>

BTW should  exit_tasks_rcu_start/stop() be defined as static inline stubs
whenever !CONFIG_TASKS_RCU ? Currently:

* if CONFIG_TASKS_RCU_GENERIC=n, the stubs are as usual (static inline)

* if CONFIG_TASKS_RCU_GENERIC=y && CONFIG_TASKS_RCU=n, then the stubs are
  defined as empty linked function (is the compiler smart enough to remove
  the empty call?)