Re: [paulmck-rcu:dev.2023.03.17a 33/38] kernel/rcu/tasks.h:140:20: warning: 'tasks_rcu_exit_srcu' defined but not used

[Liu, Yujie]

Hi Paul,

On Sun, 2023-03-19 at 17:33 -0700, Paul E. McKenney wrote:
> On Sun, Mar 19, 2023 at 03:05:43PM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2023.03.17a
> > head:   19d218a4b125a4dce12eb88097a9c55f7126ce8c
> > commit: 61eea4556e8cf92d4c9b483110a679d2652aa451 [33/38] srcu: Move work-scheduling fields from srcu_struct to srcu_usage
> > config: x86_64-kexec (https://download.01.org/0day-ci/archive/20230319/202303191536.XzMSyzTl-lkp@xxxxxxxxx/config)
> > compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
> > reproduce (this is a W=1 build):
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?id=61eea4556e8cf92d4c9b483110a679d2652aa451
> >         git remote add paulmck-rcu https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> >         git fetch --no-tags paulmck-rcu dev.2023.03.17a
> >         git checkout 61eea4556e8cf92d4c9b483110a679d2652aa451
> >         # save the config file
> >         mkdir build_dir && cp config build_dir/.config
> >         make W=1 O=build_dir ARCH=x86_64 olddefconfig
> >         make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/
> > 
> > If you fix the issue, kindly add following tag where applicable
> > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > Link: https://lore.kernel.org/oe-kbuild-all/202303191536.XzMSyzTl-lkp@xxxxxxxxx/
> > 
> > All warnings (new ones prefixed by >>):
> > 
> >    In file included from include/linux/srcu.h:49,
> >                     from include/linux/notifier.h:16,
> >                     from arch/x86/include/asm/uprobes.h:13,
> >                     from include/linux/uprobes.h:49,
> >                     from include/linux/mm_types.h:16,
> >                     from include/linux/sched/signal.h:13,
> >                     from kernel/rcu/update.c:26:
> > > > kernel/rcu/tasks.h:140:20: warning: 'tasks_rcu_exit_srcu' defined but not used [-Wunused-variable]
> >      140 | DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
> >          |                    ^~~~~~~~~~~~~~~~~~~
> >    include/linux/srcutree.h:184:38: note: in definition of macro '__DEFINE_SRCU'
> >      184 |         is_static struct srcu_struct name =                                                     \
> >          |                                      ^~~~
> >    kernel/rcu/tasks.h:140:1: note: in expansion of macro 'DEFINE_STATIC_SRCU'
> >      140 | DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
> >          | ^~~~~~~~~~~~~~~~~~
> 
> Good catch, thank you!
> 
> Does the patch shown below fix this?

We've tested the patch and the build warning is fixed by it. Thanks.

--
Best Regards,
Yujie

>                                                         Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit a9b8406e51603238941dbc6fa1437f8915254ebb
> Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Date:   Sun Mar 19 17:29:20 2023 -0700
> 
>     rcu-tasks: Fix warning for unused tasks_rcu_exit_srcu
>     
>     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@xxxxxxxxx/
>     Reported-by: kernel test robot <lkp@xxxxxxxxx>
>     Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index baf7ec178155..85a874d4166b 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -136,10 +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);
>  
> -#ifdef CONFIG_TASKS_RCU
>  /* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */
>  static void tasks_rcu_exit_srcu_stall(struct timer_list *unused);
>  static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall);
>