sched: adjust when cpu_active and cpuset configurations are updated during cpu on/offlining

Currently, when a cpu goes down, cpu_active is cleared before
CPU_DOWN_PREPARE starts and cpuset configuration is updated from a
default priority cpu notifier.  When a cpu is coming up, it's set
before CPU_ONLINE but cpuset configuration again is updated from the
same cpu notifier.

For cpu notifiers, this presents an inconsistent state.  Threads which
a CPU_DOWN_PREPARE notifier expects to be bound to the CPU can be
migrated to other cpus because the cpu is no more inactive.

Fix it by updating cpu_active in the highest priority cpu notifier and
cpuset configuration in the second highest when a cpu is coming up.
Down path is updated similarly.  This guarantees that all other cpu
notifiers see consistent cpu_active and cpuset configuration.

cpuset_track_online_cpus() notifier is converted to
cpuset_update_active_cpus() which just updates the configuration and
now called from cpuset_cpu_[in]active() notifiers registered from
sched_init_smp().  If cpuset is disabled, cpuset_update_active_cpus()
degenerates into partition_sched_domains() making separate notifier
for !CONFIG_CPUSETS unnecessary.

This problem is triggered by cmwq.  During CPU_DOWN_PREPARE, hotplug
callback creates a kthread and kthread_bind()s it to the target cpu,
and the thread is expected to run on that cpu.

* Ingo's test discovered __cpuinit/exit markups were incorrect.
  Fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Menage <menage@google.com>

5 files changed, 74 insertions, 42 deletions

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 2d9073883ea9..de6b1722cdca 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -52,6 +52,22 @@ struct notifier_block;
  * CPU notifier priorities.
  */
 enum {
+        /*
+         * SCHED_ACTIVE marks a cpu which is coming up active during
+         * CPU_ONLINE and CPU_DOWN_FAILED and must be the first
+         * notifier.  CPUSET_ACTIVE adjusts cpuset according to
+         * cpu_active mask right after SCHED_ACTIVE.  During
+         * CPU_DOWN_PREPARE, SCHED_INACTIVE and CPUSET_INACTIVE are
+         * ordered in the similar way.
+         *
+         * This ordering guarantees consistent cpu_active mask and
+         * migration behavior to all cpu notifiers.
+         */
+        CPU_PRI_SCHED_ACTIVE    = INT_MAX,
+        CPU_PRI_CPUSET_ACTIVE   = INT_MAX - 1,
+        CPU_PRI_SCHED_INACTIVE  = INT_MIN + 1,
+        CPU_PRI_CPUSET_INACTIVE = INT_MIN,
+
         /* migration should happen before other stuff but after perf */
         CPU_PRI_PERF            = 20,
         CPU_PRI_MIGRATION       = 10,
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 457ed765a116..f20eb8f16025 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -20,6 +20,7 @@ extern int number_of_cpusets;	/* How many cpusets are defined in system? */
 
 extern int cpuset_init(void);
 extern void cpuset_init_smp(void);
+extern void cpuset_update_active_cpus(void);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
 extern int cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@@ -132,6 +133,11 @@ static inline void set_mems_allowed(nodemask_t nodemask)
 static inline int cpuset_init(void) { return 0; }
 static inline void cpuset_init_smp(void) {}
 
+static inline void cpuset_update_active_cpus(void)
+{
+        partition_sched_domains(1, NULL, NULL);
+}
+
 static inline void cpuset_cpus_allowed(struct task_struct *p,
                                        struct cpumask *mask)
 {
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 97d1b426a4ac..f6e726f18491 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -235,11 +235,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
                 return -EINVAL;
 
         cpu_hotplug_begin();
-        set_cpu_active(cpu, false);
         err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
         if (err) {
-                set_cpu_active(cpu, true);
-
                 nr_calls--;
                 __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
                 printk("%s: attempt to take down CPU %u failed\n",
@@ -249,7 +246,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 
         err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
         if (err) {
-                set_cpu_active(cpu, true);
                 /* CPU didn't die: tell everyone.  Can't complain. */
                 cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
 
@@ -321,8 +317,6 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
                 goto out_notify;
         BUG_ON(!cpu_online(cpu));
 
-        set_cpu_active(cpu, true);
-
         /* Now call notifier in preparation. */
         cpu_notify(CPU_ONLINE | mod, hcpu);
 
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 02b9611eadde..05727dcaa80d 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2113,31 +2113,17 @@ static void scan_for_empty_cpusets(struct cpuset *root)
  * but making no active use of cpusets.
  *
  * This routine ensures that top_cpuset.cpus_allowed tracks
- * cpu_online_map on each CPU hotplug (cpuhp) event.
+ * cpu_active_mask on each CPU hotplug (cpuhp) event.
  *
  * Called within get_online_cpus().  Needs to call cgroup_lock()
  * before calling generate_sched_domains().
  */
-static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
-                                unsigned long phase, void *unused_cpu)
+void __cpuexit cpuset_update_active_cpus(void)
 {
         struct sched_domain_attr *attr;
         cpumask_var_t *doms;
         int ndoms;
 
-        switch (phase) {
-        case CPU_ONLINE:
-        case CPU_ONLINE_FROZEN:
-        case CPU_DOWN_PREPARE:
-        case CPU_DOWN_PREPARE_FROZEN:
-        case CPU_DOWN_FAILED:
-        case CPU_DOWN_FAILED_FROZEN:
-                break;
-
-        default:
-                return NOTIFY_DONE;
-        }
-
         cgroup_lock();
         mutex_lock(&callback_mutex);
         cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
@@ -2148,8 +2134,6 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
 
         /* Have scheduler rebuild the domains */
         partition_sched_domains(ndoms, doms, attr);
-
-        return NOTIFY_OK;
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
@@ -2203,7 +2187,6 @@ void __init cpuset_init_smp(void)
         cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
         top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
 
-        hotcpu_notifier(cpuset_track_online_cpus, 0);
         hotplug_memory_notifier(cpuset_track_online_nodes, 10);
 
         cpuset_wq = create_singlethread_workqueue("cpuset");
diff --git a/kernel/sched.c b/kernel/sched.c
index 552faf8d358c..2b942e49d0fa 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5804,17 +5804,46 @@ static struct notifier_block __cpuinitdata migration_notifier = {
         .priority = CPU_PRI_MIGRATION,
 };
 
+static int __cpuinit sched_cpu_active(struct notifier_block *nfb,
+                                      unsigned long action, void *hcpu)
+{
+        switch (action & ~CPU_TASKS_FROZEN) {
+        case CPU_ONLINE:
+        case CPU_DOWN_FAILED:
+                set_cpu_active((long)hcpu, true);
+                return NOTIFY_OK;
+        default:
+                return NOTIFY_DONE;
+        }
+}
+
+static int __cpuinit sched_cpu_inactive(struct notifier_block *nfb,
+                                        unsigned long action, void *hcpu)
+{
+        switch (action & ~CPU_TASKS_FROZEN) {
+        case CPU_DOWN_PREPARE:
+                set_cpu_active((long)hcpu, false);
+                return NOTIFY_OK;
+        default:
+                return NOTIFY_DONE;
+        }
+}
+
 static int __init migration_init(void)
 {
         void *cpu = (void *)(long)smp_processor_id();
         int err;
 
-        /* Start one for the boot CPU: */
+        /* Initialize migration for the boot CPU */
         err = migration_call(&migration_notifier, CPU_UP_PREPARE, cpu);
         BUG_ON(err == NOTIFY_BAD);
         migration_call(&migration_notifier, CPU_ONLINE, cpu);
         register_cpu_notifier(&migration_notifier);
 
+        /* Register cpu active notifiers */
+        cpu_notifier(sched_cpu_active, CPU_PRI_SCHED_ACTIVE);
+        cpu_notifier(sched_cpu_inactive, CPU_PRI_SCHED_INACTIVE);
+
         return 0;
 }
 early_initcall(migration_init);
@@ -7273,29 +7302,35 @@ int __init sched_create_sysfs_power_savings_entries(struct sysdev_class *cls)
 }
 #endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
 
-#ifndef CONFIG_CPUSETS
 /*
- * Add online and remove offline CPUs from the scheduler domains.
- * When cpusets are enabled they take over this function.
+ * Update cpusets according to cpu_active mask.  If cpusets are
+ * disabled, cpuset_update_active_cpus() becomes a simple wrapper
+ * around partition_sched_domains().
  */
-static int update_sched_domains(struct notifier_block *nfb,
-                                unsigned long action, void *hcpu)
+static int __cpuexit cpuset_cpu_active(struct notifier_block *nfb,
+                                       unsigned long action, void *hcpu)
 {
-        switch (action) {
+        switch (action & ~CPU_TASKS_FROZEN) {
         case CPU_ONLINE:
-        case CPU_ONLINE_FROZEN:
-        case CPU_DOWN_PREPARE:
-        case CPU_DOWN_PREPARE_FROZEN:
         case CPU_DOWN_FAILED:
-        case CPU_DOWN_FAILED_FROZEN:
-                partition_sched_domains(1, NULL, NULL);
+                cpuset_update_active_cpus();
                 return NOTIFY_OK;
+        default:
+                return NOTIFY_DONE;
+        }
+}
 
+static int __cpuexit cpuset_cpu_inactive(struct notifier_block *nfb,
+                                         unsigned long action, void *hcpu)
+{
+        switch (action & ~CPU_TASKS_FROZEN) {
+        case CPU_DOWN_PREPARE:
+                cpuset_update_active_cpus();
+                return NOTIFY_OK;
         default:
                 return NOTIFY_DONE;
         }
 }
-#endif
 
 static int update_runtime(struct notifier_block *nfb,
                                 unsigned long action, void *hcpu)
@@ -7341,10 +7376,8 @@ void __init sched_init_smp(void)
         mutex_unlock(&sched_domains_mutex);
         put_online_cpus();
 
-#ifndef CONFIG_CPUSETS
-        /* XXX: Theoretical race here - CPU may be hotplugged now */
-        hotcpu_notifier(update_sched_domains, 0);
-#endif
+        hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
+        hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
 
         /* RT runtime code needs to handle some hotplug events */
         hotcpu_notifier(update_runtime, 0);