cpuset: introduce effective_{cpumask|nodemask}_cpuset()

effective_cpumask_cpuset() returns an ancestor cpuset which has
non-empty cpumask.

If a cpuset is empty and the tasks in it need to update their
cpus_allowed, they take on the ancestor cpuset's cpumask.

This currently won't change any behavior, but it will later allow us
to keep tasks in empty cpusets.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 65 insertions, 11 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 2b4554588a04..82ac1f862cbc 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -791,6 +791,45 @@ void rebuild_sched_domains(void)
         mutex_unlock(&cpuset_mutex);
 }
 
+/*
+ * effective_cpumask_cpuset - return nearest ancestor with non-empty cpus
+ * @cs: the cpuset in interest
+ *
+ * A cpuset's effective cpumask is the cpumask of the nearest ancestor
+ * with non-empty cpus. We use effective cpumask whenever:
+ * - we update tasks' cpus_allowed. (they take on the ancestor's cpumask
+ *   if the cpuset they reside in has no cpus)
+ * - we want to retrieve task_cs(tsk)'s cpus_allowed.
+ *
+ * Called with cpuset_mutex held. cpuset_cpus_allowed_fallback() is an
+ * exception. See comments there.
+ */
+static struct cpuset *effective_cpumask_cpuset(struct cpuset *cs)
+{
+        while (cpumask_empty(cs->cpus_allowed))
+                cs = parent_cs(cs);
+        return cs;
+}
+
+/*
+ * effective_nodemask_cpuset - return nearest ancestor with non-empty mems
+ * @cs: the cpuset in interest
+ *
+ * A cpuset's effective nodemask is the nodemask of the nearest ancestor
+ * with non-empty memss. We use effective nodemask whenever:
+ * - we update tasks' mems_allowed. (they take on the ancestor's nodemask
+ *   if the cpuset they reside in has no mems)
+ * - we want to retrieve task_cs(tsk)'s mems_allowed.
+ *
+ * Called with cpuset_mutex held.
+ */
+static struct cpuset *effective_nodemask_cpuset(struct cpuset *cs)
+{
+        while (nodes_empty(cs->mems_allowed))
+                cs = parent_cs(cs);
+        return cs;
+}
+
 /**
  * cpuset_change_cpumask - make a task's cpus_allowed the same as its cpuset's
  * @tsk: task to test
@@ -805,7 +844,10 @@ void rebuild_sched_domains(void)
 static void cpuset_change_cpumask(struct task_struct *tsk,
                                   struct cgroup_scanner *scan)
 {
-        set_cpus_allowed_ptr(tsk, ((cgroup_cs(scan->cg))->cpus_allowed));
+        struct cpuset *cpus_cs;
+
+        cpus_cs = effective_cpumask_cpuset(cgroup_cs(scan->cg));
+        set_cpus_allowed_ptr(tsk, cpus_cs->cpus_allowed);
 }
 
 /**
@@ -920,12 +962,14 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
                                                         const nodemask_t *to)
 {
         struct task_struct *tsk = current;
+        struct cpuset *mems_cs;
 
         tsk->mems_allowed = *to;
 
         do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);
 
-        guarantee_online_mems(task_cs(tsk),&tsk->mems_allowed);
+        mems_cs = effective_nodemask_cpuset(task_cs(tsk));
+        guarantee_online_mems(mems_cs, &tsk->mems_allowed);
 }
 
 /*
@@ -1018,10 +1062,11 @@ static void update_tasks_nodemask(struct cpuset *cs, struct ptr_heap *heap)
 {
         static nodemask_t newmems;      /* protected by cpuset_mutex */
         struct cgroup_scanner scan;
+        struct cpuset *mems_cs = effective_nodemask_cpuset(cs);
 
         cpuset_being_rebound = cs;              /* causes mpol_dup() rebind */
 
-        guarantee_online_mems(cs, &newmems);
+        guarantee_online_mems(mems_cs, &newmems);
 
         scan.cg = cs->css.cgroup;
         scan.test_task = NULL;
@@ -1405,6 +1450,8 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
         struct cgroup *oldcgrp = cgroup_taskset_cur_cgroup(tset);
         struct cpuset *cs = cgroup_cs(cgrp);
         struct cpuset *oldcs = cgroup_cs(oldcgrp);
+        struct cpuset *cpus_cs = effective_cpumask_cpuset(cs);
+        struct cpuset *mems_cs = effective_nodemask_cpuset(cs);
 
         mutex_lock(&cpuset_mutex);
 
@@ -1412,9 +1459,9 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
         if (cs == &top_cpuset)
                 cpumask_copy(cpus_attach, cpu_possible_mask);
         else
-                guarantee_online_cpus(cs, cpus_attach);
+                guarantee_online_cpus(cpus_cs, cpus_attach);
 
-        guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+        guarantee_online_mems(mems_cs, &cpuset_attach_nodemask_to);
 
         cgroup_taskset_for_each(task, cgrp, tset) {
                 /*
@@ -1434,9 +1481,11 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
         cpuset_attach_nodemask_to = cs->mems_allowed;
         mm = get_task_mm(leader);
         if (mm) {
+                struct cpuset *mems_oldcs = effective_nodemask_cpuset(oldcs);
+
                 mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
                 if (is_memory_migrate(cs))
-                        cpuset_migrate_mm(mm, &oldcs->mems_allowed,
+                        cpuset_migrate_mm(mm, &mems_oldcs->mems_allowed,
                                           &cpuset_attach_nodemask_to);
                 mmput(mm);
         }
@@ -2186,20 +2235,23 @@ void __init cpuset_init_smp(void)
 
 void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 {
+        struct cpuset *cpus_cs;
+
         mutex_lock(&callback_mutex);
         task_lock(tsk);
-        guarantee_online_cpus(task_cs(tsk), pmask);
+        cpus_cs = effective_cpumask_cpuset(task_cs(tsk));
+        guarantee_online_cpus(cpus_cs, pmask);
         task_unlock(tsk);
         mutex_unlock(&callback_mutex);
 }
 
 void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
-        const struct cpuset *cs;
+        const struct cpuset *cpus_cs;
 
         rcu_read_lock();
-        cs = task_cs(tsk);
-        do_set_cpus_allowed(tsk, cs->cpus_allowed);
+        cpus_cs = effective_cpumask_cpuset(task_cs(tsk));
+        do_set_cpus_allowed(tsk, cpus_cs->cpus_allowed);
         rcu_read_unlock();
 
         /*
@@ -2238,11 +2290,13 @@ void cpuset_init_current_mems_allowed(void)
 
 nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
 {
+        struct cpuset *mems_cs;
         nodemask_t mask;
 
         mutex_lock(&callback_mutex);
         task_lock(tsk);
-        guarantee_online_mems(task_cs(tsk), &mask);
+        mems_cs = effective_nodemask_cpuset(task_cs(tsk));
+        guarantee_online_mems(mems_cs, &mask);
         task_unlock(tsk);
         mutex_unlock(&callback_mutex);