1 files changed, 25 insertions, 3 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 584bb4e6c042..794af5024c2f 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -912,6 +912,10 @@ static int update_nodemask(struct cpuset *cs, char *buf)
         int fudge;
         int retval;
 
+        /* top_cpuset.mems_allowed tracks node_online_map; it's read-only */
+        if (cs == &top_cpuset)
+                return -EACCES;
+
         trialcs = *cs;
         retval = nodelist_parse(buf, trialcs.mems_allowed);
         if (retval < 0)
@@ -2042,9 +2046,8 @@ out:
  * (of no affect) on systems that are actively using CPU hotplug
  * but making no active use of cpusets.
  *
- * This handles CPU hotplug (cpuhp) events.  If someday Memory
- * Nodes can be hotplugged (dynamically changing node_online_map)
- * then we should handle that too, perhaps in a similar way.
+ * This routine ensures that top_cpuset.cpus_allowed tracks
+ * cpu_online_map on each CPU hotplug (cpuhp) event.
  */
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -2063,6 +2066,25 @@ static int cpuset_handle_cpuhp(struct notifier_block *nb,
 }
 #endif
 
+/*
+ * Keep top_cpuset.mems_allowed tracking node_online_map.
+ * Call this routine anytime after you change node_online_map.
+ * See also the previous routine cpuset_handle_cpuhp().
+ */
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+void cpuset_track_online_nodes()
+{
+        mutex_lock(&manage_mutex);
+        mutex_lock(&callback_mutex);
+
+        top_cpuset.mems_allowed = node_online_map;
+
+        mutex_unlock(&callback_mutex);
+        mutex_unlock(&manage_mutex);
+}
+#endif
+
 /**
  * cpuset_init_smp - initialize cpus_allowed
  *