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: <5b73fe0e-bacc-4aee-a632-3160e38e42db@paulmck-laptop>
Date:   Mon, 20 Mar 2023 21:18:44 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     "Liu, Yujie" <yujie.liu@...el.com>
Cc:     lkp <lkp@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "oe-kbuild-all@...ts.linux.dev" <oe-kbuild-all@...ts.linux.dev>
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 Tue, Mar 21, 2023 at 02:49:08AM +0000, Liu, Yujie wrote:
> 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@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?
> 
> We've tested the patch and the build warning is fixed by it. Thanks.

Thank you!  May I apply your Tested-by?

							Thanx, Paul

> --
> Best Regards,
> Yujie
> 
> >                                                         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);
> > 
>