tree:   https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-5.13.y-rt-rebase
head:   7e175e6b59975c8901ad370f7818937f68de45c1
commit: 8abf1b2d2e8f61dc527e290e3cb83b0cf9fafef0 [173/222] rcu: Delay RCU-selftests
config: x86_64-randconfig-a015-20210707 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 8d69635ed9ecf36fd0ca85906bfde17949671cbe)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/?id=8abf1b2d2e8f61dc527e290e3cb83b0cf9fafef0
        git remote add linux-rt-devel https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
        git fetch --no-tags linux-rt-devel linux-5.13.y-rt-rebase
        git checkout 8abf1b2d2e8f61dc527e290e3cb83b0cf9fafef0
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from kernel/rcu/update.c:580:
>> kernel/rcu/tasks.h:1298:6: warning: no previous prototype for function 'rcu_tasks_initiate_self_tests' [-Wmissing-prototypes]
   void rcu_tasks_initiate_self_tests(void)
        ^
   kernel/rcu/tasks.h:1298:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void rcu_tasks_initiate_self_tests(void)
   ^
   static 
   1 warning generated.


vim +/rcu_tasks_initiate_self_tests +1298 kernel/rcu/tasks.h

  1297	
> 1298	void rcu_tasks_initiate_self_tests(void)
  1299	{
  1300		pr_info("Running RCU-tasks wait API self tests\n");
  1301	#ifdef CONFIG_TASKS_RCU
  1302		synchronize_rcu_tasks();
  1303		call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
  1304	#endif
  1305	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org