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: <0dfe1c60-0167-45b1-80fb-5f5400c2b1fe@paulmck-laptop>
Date:   Sun, 19 Mar 2023 10:26:26 -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);
>          | ^~~~~~~~~~~~~~~~~~

It is true that if you build a kernel with CONFIG_TASKS_RCU_GENERIC=y and
CONFIG_TASKS_RCU=n, you will get this warning.  I am at a loss as to why
this commit would have changed that, but in any case it does need a fix.

Thank you for catching it!

							Thanx, Paul

> vim +/tasks_rcu_exit_srcu +140 kernel/rcu/tasks.h
> 
> 07e105158d97b4 Paul E. McKenney 2020-03-02  138  
> eacd6f04a13331 Paul E. McKenney 2020-03-02  139  /* Track exiting tasks in order to allow them to be waited for. */
> eacd6f04a13331 Paul E. McKenney 2020-03-02 @140  DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
> eacd6f04a13331 Paul E. McKenney 2020-03-02  141  
> 
> :::::: The code at line 140 was first introduced by commit
> :::::: eacd6f04a1333187dd3e96e5635c0edce0a2e354 rcu-tasks: Move Tasks RCU to its own file
> 
> :::::: TO: Paul E. McKenney <paulmck@...nel.org>
> :::::: CC: Paul E. McKenney <paulmck@...nel.org>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests