1 files changed, 29 insertions, 3 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index c7fd2778ed50..2b4c20ab5bbe 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -325,8 +325,7 @@ 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.
@@ -335,8 +334,20 @@ 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);
 }
 
@@ -2069,6 +2080,20 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)
 	mutex_unlock(&cpuset_mutex);
 }
 
+/*
+ * Make sure the new task conform to the current state of its parent,
+ * which could have been changed by cpuset just after it inherits the
+ * state from the parent and before it sits on the cgroup's task list.
+ */
+static void cpuset_fork(struct task_struct *task)
+{
+	if (task_css_is_root(task, cpuset_cgrp_id))
+		return;
+
+	set_cpus_allowed_ptr(task, &current->cpus_allowed);
+	task->mems_allowed = current->mems_allowed;
+}
+
 struct cgroup_subsys cpuset_cgrp_subsys = {
 	.css_alloc	= cpuset_css_alloc,
 	.css_online	= cpuset_css_online,
@@ -2079,6 +2104,7 @@ struct cgroup_subsys cpuset_cgrp_subsys = {
 	.attach		= cpuset_attach,
 	.post_attach	= cpuset_post_attach,
 	.bind		= cpuset_bind,
+	.fork		= cpuset_fork,
 	.legacy_cftypes	= files,
 	.early_init	= true,
 };