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

[kbuild test robot <lkp@intel.com>]

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 <lkp@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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