[luto:sched/lazymm 13/16] kernel/sched/core.c:4986:22: warning: variable 'old_active_mm' is uninitialized when used here

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git sched/lazymm
head:   c0d03d4f2778fd0a7c16e69cdfb3f111296129b5
commit: 4863118ffa6fe6af7cfb18c4d4ee6434537b0c8b [13/16] sched, exec: Factor current mm changes out from exec
config: x86_64-randconfig-r034-20211116 (attached as .config)
compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project fbe72e41b99dc7994daac300d208a955be3e4a0a)
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
        # https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?id=4863118ffa6fe6af7cfb18c4d4ee6434537b0c8b
        git remote add luto https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git
        git fetch --no-tags luto sched/lazymm
        git checkout 4863118ffa6fe6af7cfb18c4d4ee6434537b0c8b
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=x86_64 

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

All warnings (new ones prefixed by >>):

   kernel/sched/core.c:3417:6: warning: no previous prototype for function 'sched_set_stop_task' [-Wmissing-prototypes]
   void sched_set_stop_task(int cpu, struct task_struct *stop)
        ^
   kernel/sched/core.c:3417:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void sched_set_stop_task(int cpu, struct task_struct *stop)
   ^
   static 
>> kernel/sched/core.c:4986:22: warning: variable 'old_active_mm' is uninitialized when used here [-Wuninitialized]
                   switch_mm_irqs_off(old_active_mm, mm, tsk);
                                      ^~~~~~~~~~~~~
   kernel/sched/core.c:4941:33: note: initialize the variable 'old_active_mm' to silence this warning
           struct mm_struct *old_active_mm, *mm_to_drop = NULL;
                                          ^
                                           = NULL
   2 warnings generated.


vim +/old_active_mm +4986 kernel/sched/core.c

  4937	
  4938	void __change_current_mm(struct mm_struct *mm, bool mm_is_brand_new)
  4939	{
  4940		struct task_struct *tsk = current;
  4941		struct mm_struct *old_active_mm, *mm_to_drop = NULL;
  4942	
  4943		BUG_ON(!mm);	/* likely to cause corruption if we continue */
  4944	
  4945		/*
  4946		 * We do not want to schedule, nor should procfs peek at current->mm
  4947		 * while we're modifying it.  task_lock() disables preemption and
  4948		 * locks against procfs.
  4949		 */
  4950		task_lock(tsk);
  4951		/*
  4952		 * membarrier() requires a full barrier before switching mm.
  4953		 */
  4954		smp_mb__after_spinlock();
  4955	
  4956		local_irq_disable();
  4957	
  4958		if (tsk->mm) {
  4959			/* We're detaching from an old mm.  Sync stats. */
  4960			sync_mm_rss(tsk->mm);
  4961		} else {
  4962			/*
  4963			 * Switching from kernel mm to user.  Drop the old lazy
  4964			 * mm reference.
  4965			 */
  4966			mm_to_drop = tsk->active_mm;
  4967		}
  4968	
  4969		tsk->active_mm = mm;
  4970		WRITE_ONCE(tsk->mm, mm);  /* membarrier reads this without locks */
  4971		membarrier_update_current_mm(mm);
  4972	
  4973		if (mm_is_brand_new) {
  4974			/*
  4975			 * For historical reasons, some architectures want IRQs on
  4976			 * when activate_mm() is called.  If we're going to call
  4977			 * activate_mm(), turn on IRQs but leave preemption
  4978			 * disabled.
  4979			 */
  4980			if (!IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
  4981				local_irq_enable();
  4982			activate_mm(old_active_mm, mm);
  4983			if (IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
  4984				local_irq_enable();
  4985		} else {
> 4986			switch_mm_irqs_off(old_active_mm, mm, tsk);
  4987			local_irq_enable();
  4988		}
  4989	
  4990		/* IRQs are on now.  Preemption is still disabled by task_lock(). */
  4991	
  4992		membarrier_finish_switch_mm(mm);
  4993		vmacache_flush(tsk);
  4994		task_unlock(tsk);
  4995	

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

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