Merge branch 'for-4.8-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj...

Pull cgroup fixes from Tejun Heo:
 "Three late fixes for cgroup: Two cpuset ones, one trivial and the
  other pretty obscure, and a cgroup core fix for a bug which impacts
  cgroup v2 namespace users"

* 'for-4.8-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: fix invalid controller enable rejections with cgroup namespace
  cpuset: fix non static symbol warning
  cpuset: handle race between CPU hotplug and cpuset_hotplug_work

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5e8dab5..d6b729b 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3446,9 +3446,28 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
         * Except for the root, subtree_control must be zero for a cgroup
         * with tasks so that child cgroups don't compete against tasks.
         */
-       if (enable && cgroup_parent(cgrp) && !list_empty(&cgrp->cset_links)) {
-               ret = -EBUSY;
-               goto out_unlock;
+       if (enable && cgroup_parent(cgrp)) {
+               struct cgrp_cset_link *link;
+
+               /*
+                * Because namespaces pin csets too, @cgrp->cset_links
+                * might not be empty even when @cgrp is empty.  Walk and
+                * verify each cset.
+                */
+               spin_lock_irq(&css_set_lock);
+
+               ret = 0;
+               list_for_each_entry(link, &cgrp->cset_links, cset_link) {
+                       if (css_set_populated(link->cset)) {
+                               ret = -EBUSY;
+                               break;
+                       }
+               }
+
+               spin_unlock_irq(&css_set_lock);
+
+               if (ret)
+                       goto out_unlock;
        }
 
        /* save and update control masks and prepare csses */
@@ -3899,7 +3918,9 @@ void cgroup_file_notify(struct cgroup_file *cfile)
  * cgroup_task_count - count the number of tasks in a cgroup.
  * @cgrp: the cgroup in question
  *
- * Return the number of tasks in the cgroup.
+ * Return the number of tasks in the cgroup.  The returned number can be
+ * higher than the actual number of tasks due to css_set references from
+ * namespace roots and temporary usages.
  */
 static int cgroup_task_count(const struct cgroup *cgrp)
 {

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index c27e533..2b4c20a 100644 (file)
--- 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);
 }
 
@@ -2074,7 +2085,7 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)
  * 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.
  */
-void cpuset_fork(struct task_struct *task)
+static void cpuset_fork(struct task_struct *task)
 {
        if (task_css_is_root(task, cpuset_cgrp_id))
                return;