1 files changed, 92 insertions, 38 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 8c8bd652dd12..f33c7153b6d7 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -147,6 +147,12 @@ typedef enum {
         CS_SPREAD_SLAB,
 } cpuset_flagbits_t;
 
+/* the type of hotplug event */
+enum hotplug_event {
+        CPUSET_CPU_OFFLINE,
+        CPUSET_MEM_OFFLINE,
+};
+
 /* convenient tests for these bits */
 static inline int is_cpu_exclusive(const struct cpuset *cs)
 {
@@ -1990,8 +1996,36 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
 }
 
 /*
- * Walk the specified cpuset subtree and look for empty cpusets.
- * The tasks of such cpuset must be moved to a parent cpuset.
+ * Helper function to traverse cpusets.
+ * It can be used to walk the cpuset tree from top to bottom, completing
+ * one layer before dropping down to the next (thus always processing a
+ * node before any of its children).
+ */
+static struct cpuset *cpuset_next(struct list_head *queue)
+{
+        struct cpuset *cp;
+        struct cpuset *child;   /* scans child cpusets of cp */
+        struct cgroup *cont;
+
+        if (list_empty(queue))
+                return NULL;
+
+        cp = list_first_entry(queue, struct cpuset, stack_list);
+        list_del(queue->next);
+        list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
+                child = cgroup_cs(cont);
+                list_add_tail(&child->stack_list, queue);
+        }
+
+        return cp;
+}
+
+
+/*
+ * Walk the specified cpuset subtree upon a hotplug operation (CPU/Memory
+ * online/offline) and update the cpusets accordingly.
+ * For regular CPU/Mem hotplug, look for empty cpusets; the tasks of such
+ * cpuset must be moved to a parent cpuset.
  *
  * Called with cgroup_mutex held.  We take callback_mutex to modify
  * cpus_allowed and mems_allowed.
@@ -2000,50 +2034,61 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
  * before dropping down to the next.  It always processes a node before
  * any of its children.
  *
- * For now, since we lack memory hot unplug, we'll never see a cpuset
- * that has tasks along with an empty 'mems'.  But if we did see such
- * a cpuset, we'd handle it just like we do if its 'cpus' was empty.
+ * In the case of memory hot-unplug, it will remove nodes from N_HIGH_MEMORY
+ * if all present pages from a node are offlined.
  */
-static void scan_for_empty_cpusets(struct cpuset *root)
+static void
+scan_cpusets_upon_hotplug(struct cpuset *root, enum hotplug_event event)
 {
         LIST_HEAD(queue);
-        struct cpuset *cp;      /* scans cpusets being updated */
-        struct cpuset *child;   /* scans child cpusets of cp */
-        struct cgroup *cont;
+        struct cpuset *cp;              /* scans cpusets being updated */
         static nodemask_t oldmems;      /* protected by cgroup_mutex */
 
         list_add_tail((struct list_head *)&root->stack_list, &queue);
 
-        while (!list_empty(&queue)) {
-                cp = list_first_entry(&queue, struct cpuset, stack_list);
-                list_del(queue.next);
-                list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
-                        child = cgroup_cs(cont);
-                        list_add_tail(&child->stack_list, &queue);
+        switch (event) {
+        case CPUSET_CPU_OFFLINE:
+                while ((cp = cpuset_next(&queue)) != NULL) {
+
+                        /* Continue past cpusets with all cpus online */
+                        if (cpumask_subset(cp->cpus_allowed, cpu_active_mask))
+                                continue;
+
+                        /* Remove offline cpus from this cpuset. */
+                        mutex_lock(&callback_mutex);
+                        cpumask_and(cp->cpus_allowed, cp->cpus_allowed,
+                                                        cpu_active_mask);
+                        mutex_unlock(&callback_mutex);
+
+                        /* Move tasks from the empty cpuset to a parent */
+                        if (cpumask_empty(cp->cpus_allowed))
+                                remove_tasks_in_empty_cpuset(cp);
+                        else
+                                update_tasks_cpumask(cp, NULL);
                 }
+                break;
 
-                /* Continue past cpusets with all cpus, mems online */
-                if (cpumask_subset(cp->cpus_allowed, cpu_active_mask) &&
-                    nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
-                        continue;
+        case CPUSET_MEM_OFFLINE:
+                while ((cp = cpuset_next(&queue)) != NULL) {
 
-                oldmems = cp->mems_allowed;
+                        /* Continue past cpusets with all mems online */
+                        if (nodes_subset(cp->mems_allowed,
+                                        node_states[N_HIGH_MEMORY]))
+                                continue;
 
-                /* Remove offline cpus and mems from this cpuset. */
-                mutex_lock(&callback_mutex);
-                cpumask_and(cp->cpus_allowed, cp->cpus_allowed,
-                            cpu_active_mask);
-                nodes_and(cp->mems_allowed, cp->mems_allowed,
+                        oldmems = cp->mems_allowed;
+
+                        /* Remove offline mems from this cpuset. */
+                        mutex_lock(&callback_mutex);
+                        nodes_and(cp->mems_allowed, cp->mems_allowed,
                                                 node_states[N_HIGH_MEMORY]);
-                mutex_unlock(&callback_mutex);
+                        mutex_unlock(&callback_mutex);
 
-                /* Move tasks from the empty cpuset to a parent */
-                if (cpumask_empty(cp->cpus_allowed) ||
-                     nodes_empty(cp->mems_allowed))
-                        remove_tasks_in_empty_cpuset(cp);
-                else {
-                        update_tasks_cpumask(cp, NULL);
-                        update_tasks_nodemask(cp, &oldmems, NULL);
+                        /* Move tasks from the empty cpuset to a parent */
+                        if (nodes_empty(cp->mems_allowed))
+                                remove_tasks_in_empty_cpuset(cp);
+                        else
+                                update_tasks_nodemask(cp, &oldmems, NULL);
                 }
         }
 }
@@ -2054,13 +2099,19 @@ static void scan_for_empty_cpusets(struct cpuset *root)
  * (of no affect) on systems that are actively using CPU hotplug
  * but making no active use of cpusets.
  *
+ * The only exception to this is suspend/resume, where we don't
+ * modify cpusets at all.
+ *
  * This routine ensures that top_cpuset.cpus_allowed tracks
  * cpu_active_mask on each CPU hotplug (cpuhp) event.
  *
  * Called within get_online_cpus().  Needs to call cgroup_lock()
  * before calling generate_sched_domains().
+ *
+ * @cpu_online: Indicates whether this is a CPU online event (true) or
+ * a CPU offline event (false).
  */
-void cpuset_update_active_cpus(void)
+void cpuset_update_active_cpus(bool cpu_online)
 {
         struct sched_domain_attr *attr;
         cpumask_var_t *doms;
@@ -2070,7 +2121,10 @@ void cpuset_update_active_cpus(void)
         mutex_lock(&callback_mutex);
         cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
         mutex_unlock(&callback_mutex);
-        scan_for_empty_cpusets(&top_cpuset);
+
+        if (!cpu_online)
+                scan_cpusets_upon_hotplug(&top_cpuset, CPUSET_CPU_OFFLINE);
+
         ndoms = generate_sched_domains(&doms, &attr);
         cgroup_unlock();
 
@@ -2082,7 +2136,7 @@ void cpuset_update_active_cpus(void)
 /*
  * Keep top_cpuset.mems_allowed tracking node_states[N_HIGH_MEMORY].
  * Call this routine anytime after node_states[N_HIGH_MEMORY] changes.
- * See also the previous routine cpuset_track_online_cpus().
+ * See cpuset_update_active_cpus() for CPU hotplug handling.
  */
 static int cpuset_track_online_nodes(struct notifier_block *self,
                                 unsigned long action, void *arg)
@@ -2101,9 +2155,9 @@ static int cpuset_track_online_nodes(struct notifier_block *self,
         case MEM_OFFLINE:
                 /*
                  * needn't update top_cpuset.mems_allowed explicitly because
-                 * scan_for_empty_cpusets() will update it.
+                 * scan_cpusets_upon_hotplug() will update it.
                  */
-                scan_for_empty_cpusets(&top_cpuset);
+                scan_cpusets_upon_hotplug(&top_cpuset, CPUSET_MEM_OFFLINE);
                 break;
         default:
                 break;