cpuset: replace cpuset->stack_list with cpuset_for_each_descendant_pre()

Implement cpuset_for_each_descendant_pre() and replace the
cpuset-specific tree walking using cpuset->stack_list with it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 48 insertions, 75 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 5e348ae37ce9..0ddb48d40e4d 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -103,9 +103,6 @@ struct cpuset {
         /* for custom sched domain */
         int relax_domain_level;
 
-        /* used for walking a cpuset hierarchy */
-        struct list_head stack_list;
-
         struct work_struct hotplug_work;
 };
 
@@ -207,6 +204,20 @@ static struct cpuset top_cpuset = {
         cgroup_for_each_child((pos_cgrp), (parent_cs)->css.cgroup)      \
                 if (is_cpuset_online(((child_cs) = cgroup_cs((pos_cgrp)))))
 
+/**
+ * cpuset_for_each_descendant_pre - pre-order walk of a cpuset's descendants
+ * @des_cs: loop cursor pointing to the current descendant
+ * @pos_cgrp: used for iteration
+ * @root_cs: target cpuset to walk ancestor of
+ *
+ * Walk @des_cs through the online descendants of @root_cs.  Must be used
+ * with RCU read locked.  The caller may modify @pos_cgrp by calling
+ * cgroup_rightmost_descendant() to skip subtree.
+ */
+#define cpuset_for_each_descendant_pre(des_cs, pos_cgrp, root_cs)       \
+        cgroup_for_each_descendant_pre((pos_cgrp), (root_cs)->css.cgroup) \
+                if (is_cpuset_online(((des_cs) = cgroup_cs((pos_cgrp)))))
+
 /*
  * There are two global mutexes guarding cpuset structures - cpuset_mutex
  * and callback_mutex.  The latter may nest inside the former.  We also
@@ -507,31 +518,24 @@ update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
         return;
 }
 
-static void
-update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
+static void update_domain_attr_tree(struct sched_domain_attr *dattr,
+                                    struct cpuset *root_cs)
 {
-        LIST_HEAD(q);
-
-        list_add(&c->stack_list, &q);
-        while (!list_empty(&q)) {
-                struct cpuset *cp;
-                struct cgroup *cont;
-                struct cpuset *child;
-
-                cp = list_first_entry(&q, struct cpuset, stack_list);
-                list_del(q.next);
+        struct cpuset *cp;
+        struct cgroup *pos_cgrp;
 
-                if (cpumask_empty(cp->cpus_allowed))
+        rcu_read_lock();
+        cpuset_for_each_descendant_pre(cp, pos_cgrp, root_cs) {
+                /* skip the whole subtree if @cp doesn't have any CPU */
+                if (cpumask_empty(cp->cpus_allowed)) {
+                        pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
                         continue;
+                }
 
                 if (is_sched_load_balance(cp))
                         update_domain_attr(dattr, cp);
-
-                rcu_read_lock();
-                cpuset_for_each_child(child, cont, cp)
-                        list_add_tail(&child->stack_list, &q);
-                rcu_read_unlock();
         }
+        rcu_read_unlock();
 }
 
 /*
@@ -591,7 +595,6 @@ update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
 static int generate_sched_domains(cpumask_var_t **domains,
                         struct sched_domain_attr **attributes)
 {
-        LIST_HEAD(q);           /* queue of cpusets to be scanned */
         struct cpuset *cp;      /* scans q */
         struct cpuset **csa;    /* array of all cpuset ptrs */
         int csn;                /* how many cpuset ptrs in csa so far */
@@ -600,6 +603,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
         struct sched_domain_attr *dattr;  /* attributes for custom domains */
         int ndoms = 0;          /* number of sched domains in result */
         int nslot;              /* next empty doms[] struct cpumask slot */
+        struct cgroup *pos_cgrp;
 
         doms = NULL;
         dattr = NULL;
@@ -627,33 +631,27 @@ static int generate_sched_domains(cpumask_var_t **domains,
                 goto done;
         csn = 0;
 
-        list_add(&top_cpuset.stack_list, &q);
-        while (!list_empty(&q)) {
-                struct cgroup *cont;
-                struct cpuset *child;   /* scans child cpusets of cp */
-
-                cp = list_first_entry(&q, struct cpuset, stack_list);
-                list_del(q.next);
-
-                if (cpumask_empty(cp->cpus_allowed))
-                        continue;
-
+        rcu_read_lock();
+        cpuset_for_each_descendant_pre(cp, pos_cgrp, &top_cpuset) {
                 /*
-                 * All child cpusets contain a subset of the parent's cpus, so
-                 * just skip them, and then we call update_domain_attr_tree()
-                 * to calc relax_domain_level of the corresponding sched
-                 * domain.
+                 * Continue traversing beyond @cp iff @cp has some CPUs and
+                 * isn't load balancing.  The former is obvious.  The
+                 * latter: All child cpusets contain a subset of the
+                 * parent's cpus, so just skip them, and then we call
+                 * update_domain_attr_tree() to calc relax_domain_level of
+                 * the corresponding sched domain.
                  */
-                if (is_sched_load_balance(cp)) {
-                        csa[csn++] = cp;
+                if (!cpumask_empty(cp->cpus_allowed) &&
+                    !is_sched_load_balance(cp))
                         continue;
-                }
 
-                rcu_read_lock();
-                cpuset_for_each_child(child, cont, cp)
-                        list_add_tail(&child->stack_list, &q);
-                rcu_read_unlock();
-        }
+                if (is_sched_load_balance(cp))
+                        csa[csn++] = cp;
+
+                /* skip @cp's subtree */
+                pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
+        }
+        rcu_read_unlock();
 
         for (i = 0; i < csn; i++)
                 csa[i]->pn = i;
@@ -2068,31 +2066,6 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
         move_member_tasks_to_cpuset(cs, parent);
 }
 
-/*
- * 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);
-        rcu_read_lock();
-        cpuset_for_each_child(child, cont, cp)
-                list_add_tail(&child->stack_list, queue);
-        rcu_read_unlock();
-
-        return cp;
-}
-
 /**
  * cpuset_propagate_hotplug_workfn - propagate CPU/memory hotplug to a cpuset
  * @cs: cpuset in interest
@@ -2229,12 +2202,12 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
         /* if cpus or mems went down, we need to propagate to descendants */
         if (cpus_offlined || mems_offlined) {
                 struct cpuset *cs;
-                LIST_HEAD(queue);
+                struct cgroup *pos_cgrp;
 
-                list_add_tail(&top_cpuset.stack_list, &queue);
-                while ((cs = cpuset_next(&queue)))
-                        if (cs != &top_cpuset)
-                                schedule_cpuset_propagate_hotplug(cs);
+                rcu_read_lock();
+                cpuset_for_each_descendant_pre(cs, pos_cgrp, &top_cpuset)
+                        schedule_cpuset_propagate_hotplug(cs);
+                rcu_read_unlock();
         }
 
         mutex_unlock(&cpuset_mutex);