linux-kernel - Re: [paulmck-rcu:dev.2023.03.17a 33/38] kernel/rcu/tasks.h:140:20: warning: 'tasks_rcu_exit

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Message-ID: <be0bf772-bac1-4a18-a46a-922a93093314@paulmck-laptop>
Date:   Sun, 19 Mar 2023 17:33:58 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     kernel test robot <lkp@...el.com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [paulmck-rcu:dev.2023.03.17a 33/38] kernel/rcu/tasks.h:140:20:
 warning: 'tasks_rcu_exit_srcu' defined but not used

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@intel.com/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@...el.com>
> | Link: https://lore.kernel.org/oe-kbuild-all/202303191536.XzMSyzTl-lkp@intel.com/
> 
> 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?

							Thanx, Paul

------------------------------------------------------------------------

commit a9b8406e51603238941dbc6fa1437f8915254ebb
Author: Paul E. McKenney <paulmck@...nel.org>
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@intel.com/
    Reported-by: kernel test robot <lkp@...el.com>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

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);