2 files changed, 25 insertions, 5 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index de7b3b217772..dbb1043e8656 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -839,7 +839,17 @@ struct sched_group {
          */
         u32 reciprocal_cpu_power;
 
-        unsigned long cpumask[];
+        /*
+         * The CPUs this group covers.
+         *
+         * NOTE: this field is variable length. (Allocated dynamically
+         * by attaching extra space to the end of the structure,
+         * depending on how many CPUs the kernel has booted up with)
+         *
+         * It is also be embedded into static data structures at build
+         * time. (See 'struct static_sched_group' in kernel/sched.c)
+         */
+        unsigned long cpumask[0];
 };
 
 static inline struct cpumask *sched_group_cpus(struct sched_group *sg)
@@ -925,8 +935,17 @@ struct sched_domain {
         char *name;
 #endif
 
-        /* span of all CPUs in this domain */
-        unsigned long span[];
+        /*
+         * Span of all CPUs in this domain.
+         *
+         * NOTE: this field is variable length. (Allocated dynamically
+         * by attaching extra space to the end of the structure,
+         * depending on how many CPUs the kernel has booted up with)
+         *
+         * It is also be embedded into static data structures at build
+         * time. (See 'struct static_sched_domain' in kernel/sched.c)
+         */
+        unsigned long span[0];
 };
 
 static inline struct cpumask *sched_domain_span(struct sched_domain *sd)
diff --git a/kernel/sched.c b/kernel/sched.c
index 497c09ba61e7..228acae8821f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7948,8 +7948,9 @@ int sched_smt_power_savings = 0, sched_mc_power_savings = 0;
 
 /*
  * The cpus mask in sched_group and sched_domain hangs off the end.
- * FIXME: use cpumask_var_t or dynamic percpu alloc to avoid wasting space
- * for nr_cpu_ids < CONFIG_NR_CPUS.
+ *
+ * ( See the the comments in include/linux/sched.h:struct sched_group
+ *   and struct sched_domain. )
  */
 struct static_sched_group {
         struct sched_group sg;