Re: [PATCH 3/3] task: Clean house now that tasks on the runqueue are rcu protected

[kbuild test robot]

Hi "Eric,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[cannot apply to v5.3-rc7 next-20190902]
[if your patch is applied to the wrong git tree, please drop us a note to help 
improve the system]

url:    
https://github.com/0day-ci/linux/commits/Eric-W-Biederman/task-Making-tasks-on-the-runqueue-rcu-protected/20190903-130546
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.1-rc1-7-g2b96cd8-dirty
        make ARCH=x86_64 allmodconfig
        make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <l...@intel.com>


sparse warnings: (new ones prefixed by >>)

>> kernel/sched/membarrier.c:74:21: sparse: sparse: incompatible types in 
>> comparison expression (different address spaces):
>> kernel/sched/membarrier.c:74:21: sparse:    struct task_struct [noderef] 
>> <asn:4> *
>> kernel/sched/membarrier.c:74:21: sparse:    struct task_struct *
   kernel/sched/membarrier.c:153:21: sparse: sparse: incompatible types in 
comparison expression (different address spaces):
   kernel/sched/membarrier.c:153:21: sparse:    struct task_struct [noderef] 
<asn:4> *
   kernel/sched/membarrier.c:153:21: sparse:    struct task_struct *

vim +74 kernel/sched/membarrier.c

    32  
    33  static int membarrier_global_expedited(void)
    34  {
    35          int cpu;
    36          bool fallback = false;
    37          cpumask_var_t tmpmask;
    38  
    39          if (num_online_cpus() == 1)
    40                  return 0;
    41  
    42          /*
    43           * Matches memory barriers around rq->curr modification in
    44           * scheduler.
    45           */
    46          smp_mb();       /* system call entry is not a mb. */
    47  
    48          /*
    49           * Expedited membarrier commands guarantee that they won't
    50           * block, hence the GFP_NOWAIT allocation flag and fallback
    51           * implementation.
    52           */
    53          if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
    54                  /* Fallback for OOM. */
    55                  fallback = true;
    56          }
    57  
    58          cpus_read_lock();
    59          for_each_online_cpu(cpu) {
    60                  struct task_struct *p;
    61  
    62                  /*
    63                   * Skipping the current CPU is OK even through we can be
    64                   * migrated at any point. The current CPU, at the point
    65                   * where we read raw_smp_processor_id(), is ensured to
    66                   * be in program order with respect to the caller
    67                   * thread. Therefore, we can skip this CPU from the
    68                   * iteration.
    69                   */
    70                  if (cpu == raw_smp_processor_id())
    71                          continue;
    72  
    73                  rcu_read_lock();
  > 74                  p = rcu_dereference(cpu_rq(cpu)->curr);
    75                  if (p && p->mm && 
(atomic_read(&p->mm->membarrier_state) &
    76                                     MEMBARRIER_STATE_GLOBAL_EXPEDITED)) {
    77                          if (!fallback)
    78                                  __cpumask_set_cpu(cpu, tmpmask);
    79                          else
    80                                  smp_call_function_single(cpu, ipi_mb, 
NULL, 1);
    81                  }
    82                  rcu_read_unlock();
    83          }
    84          if (!fallback) {
    85                  preempt_disable();
    86                  smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
    87                  preempt_enable();
    88                  free_cpumask_var(tmpmask);
    89          }
    90          cpus_read_unlock();
    91  
    92          /*
    93           * Memory barrier on the caller thread _after_ we finished
    94           * waiting for the last IPI. Matches memory barriers around
    95           * rq->curr modification in scheduler.
    96           */
    97          smp_mb();       /* exit from system call is not a mb */
    98          return 0;
    99  }
   100  

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