[bug report] perf: Add Arm CMN-600 PMU driver

[Dan Carpenter]

Hello Robin Murphy,

The patch 0ba64770a2f2: "perf: Add Arm CMN-600 PMU driver" from Sep
18, 2020, leads to the following static checker warning:

	drivers/perf/arm-cmn.c:1156 arm_cmn_pmu_offline_cpu()
	error: potential NULL dereference 'cmn'.

drivers/perf/arm-cmn.c
  1150  static int arm_cmn_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
  1151  {
  1152          struct arm_cmn *cmn;
  1153          unsigned int target;
  1154  
  1155          cmn = hlist_entry_safe(node, struct arm_cmn, cpuhp_node);
  1156          if (cpu != cmn->cpu)
                           ^^^^^^^^
It doesn't make sense to use hlist_entry_safe() and then dereference
"cmn" without checking for NULL.  It should either be hlist_entry() or
there should be a NULL check.

  1157                  return 0;
  1158  
  1159          target = cpumask_any_but(cpu_online_mask, cpu);
  1160          if (target >= nr_cpu_ids)
  1161                  return 0;
  1162  
  1163          perf_pmu_migrate_context(&cmn->pmu, cpu, target);
  1164          cmn->cpu = target;
  1165          return 0;
  1166  }

regards,
dan carpenter