1 files changed, 35 insertions, 4 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 3d448e646a4a..658eb1a32084 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -260,6 +260,13 @@ static char cpuset_nodelist[CPUSET_NODELIST_LEN];
 static DEFINE_SPINLOCK(cpuset_buffer_lock);
 
 /*
+ * CPU / memory hotplug is handled asynchronously.
+ */
+static void cpuset_hotplug_workfn(struct work_struct *work);
+
+static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);
+
+/*
  * This is ugly, but preserves the userspace API for existing cpuset
  * users. If someone tries to mount the "cpuset" filesystem, we
  * silently switch it to mount "cgroup" instead
@@ -1565,6 +1572,19 @@ static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
         struct cpuset *cs = cgroup_cs(cgrp);
         struct cpuset *trialcs;
 
+        /*
+         * CPU or memory hotunplug may leave @cs w/o any execution
+         * resources, in which case the hotplug code asynchronously updates
+         * configuration and transfers all tasks to the nearest ancestor
+         * which can execute.
+         *
+         * As writes to "cpus" or "mems" may restore @cs's execution
+         * resources, wait for the previously scheduled operations before
+         * proceeding, so that we don't end up keep removing tasks added
+         * after execution capability is restored.
+         */
+        flush_work(&cpuset_hotplug_work);
+
         if (!cgroup_lock_live_group(cgrp))
                 return -ENODEV;
 
@@ -2095,7 +2115,7 @@ static void cpuset_propagate_hotplug(struct cpuset *cs)
 }
 
 /**
- * cpuset_handle_hotplug - handle CPU/memory hot[un]plug
+ * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
  *
  * This function is called after either CPU or memory configuration has
  * changed and updates cpuset accordingly.  The top_cpuset is always
@@ -2110,7 +2130,7 @@ static void cpuset_propagate_hotplug(struct cpuset *cs)
  * Note that CPU offlining during suspend is ignored.  We don't modify
  * cpusets across suspend/resume cycles at all.
  */
-static void cpuset_handle_hotplug(void)
+static void cpuset_hotplug_workfn(struct work_struct *work)
 {
         static cpumask_t new_cpus, tmp_cpus;
         static nodemask_t new_mems, tmp_mems;
@@ -2177,7 +2197,18 @@ static void cpuset_handle_hotplug(void)
 
 void cpuset_update_active_cpus(bool cpu_online)
 {
-        cpuset_handle_hotplug();
+        /*
+         * We're inside cpu hotplug critical region which usually nests
+         * inside cgroup synchronization.  Bounce actual hotplug processing
+         * to a work item to avoid reverse locking order.
+         *
+         * We still need to do partition_sched_domains() synchronously;
+         * otherwise, the scheduler will get confused and put tasks to the
+         * dead CPU.  Fall back to the default single domain.
+         * cpuset_hotplug_workfn() will rebuild it as necessary.
+         */
+        partition_sched_domains(1, NULL, NULL);
+        schedule_work(&cpuset_hotplug_work);
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
@@ -2189,7 +2220,7 @@ void cpuset_update_active_cpus(bool cpu_online)
 static int cpuset_track_online_nodes(struct notifier_block *self,
                                 unsigned long action, void *arg)
 {
-        cpuset_handle_hotplug();
+        schedule_work(&cpuset_hotplug_work);
         return NOTIFY_OK;
 }
 #endif