kernel/sched/psi.c:639:13: warning: 'rq' may be used uninitialized in this function

[kbuild test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
master
head:   651022382c7f8da46cb4872a545ee1da6d097d2a
commit: 2ce7135adc9ad081aa3c49744144376ac74fea60 psi: cgroup support
date:   9 days ago
config: x86_64-randconfig-s1-11051307 (attached as .config)
compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026
reproduce:
        git checkout 2ce7135adc9ad081aa3c49744144376ac74fea60
        # save the attached .config to linux build tree
        make ARCH=x86_64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   kernel/sched/psi.c: In function 'cgroup_move_task':
>> kernel/sched/psi.c:639:13: warning: 'rq' may be used uninitialized in this 
>> function [-Wmaybe-uninitialized]
     struct rq *rq;
                ^~

vim +/rq +639 kernel/sched/psi.c

   621  
   622  /**
   623   * cgroup_move_task - move task to a different cgroup
   624   * @task: the task
   625   * @to: the target css_set
   626   *
   627   * Move task to a new cgroup and safely migrate its associated stall
   628   * state between the different groups.
   629   *
   630   * This function acquires the task's rq lock to lock out concurrent
   631   * changes to the task's scheduling state and - in case the task is
   632   * running - concurrent changes to its stall state.
   633   */
   634  void cgroup_move_task(struct task_struct *task, struct css_set *to)
   635  {
   636          bool move_psi = !psi_disabled;
   637          unsigned int task_flags = 0;
   638          struct rq_flags rf;
 > 639          struct rq *rq;
   640  
   641          if (move_psi) {
   642                  rq = task_rq_lock(task, &rf);
   643  
   644                  if (task_on_rq_queued(task))
   645                          task_flags = TSK_RUNNING;
   646                  else if (task->in_iowait)
   647                          task_flags = TSK_IOWAIT;
   648  
   649                  if (task->flags & PF_MEMSTALL)
   650                          task_flags |= TSK_MEMSTALL;
   651  
   652                  if (task_flags)
   653                          psi_task_change(task, task_flags, 0);
   654          }
   655  
   656          /*
   657           * Lame to do this here, but the scheduler cannot be locked
   658           * from the outside, so we move cgroups from inside sched/.
   659           */
   660          rcu_assign_pointer(task->cgroups, to);
   661  
   662          if (move_psi) {
   663                  if (task_flags)
   664                          psi_task_change(task, 0, task_flags);
   665  
   666                  task_rq_unlock(rq, task, &rf);
   667          }
   668  }
   669  #endif /* CONFIG_CGROUPS */
   670  

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