cpuset: handle race between CPU hotplug and cpuset_hotplug_work

[firefly-linux-kernel-4.4.55.git] / kernel / cpuset.c

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index b9279a2844d81656115195235df679ff2b2291e0..b271353d5202ba4fa2e8f9d469e1efd4307cf609 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -324,8 +324,7 @@ static struct file_system_type cpuset_fs_type = {
 /*
  * Return in pmask the portion of a cpusets's cpus_allowed that
  * are online.  If none are online, walk up the cpuset hierarchy
- * until we find one that does have some online cpus.  The top
- * cpuset always has some cpus online.
+ * until we find one that does have some online cpus.
  *
  * One way or another, we guarantee to return some non-empty subset
  * of cpu_online_mask.
@@ -334,8 +333,20 @@ static struct file_system_type cpuset_fs_type = {
  */
 static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
 {
-       while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask))
+       while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) {
                cs = parent_cs(cs);
+               if (unlikely(!cs)) {
+                       /*
+                        * The top cpuset doesn't have any online cpu as a
+                        * consequence of a race between cpuset_hotplug_work
+                        * and cpu hotplug notifier.  But we know the top
+                        * cpuset's effective_cpus is on its way to to be
+                        * identical to cpu_online_mask.
+                        */
+                       cpumask_copy(pmask, cpu_online_mask);
+                       return;
+               }
+       }
        cpumask_and(pmask, cs->effective_cpus, cpu_online_mask);
 }