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

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>

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 2d90738..de6b172 100644 (file)
--- 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 457ed76..f20eb8f 100644 (file)
--- 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 97d1b42..f6e726f 100644 (file)
--- 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 02b9611..05727dc 100644 (file)
--- 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 552faf8..2b942e4 100644 (file)
--- 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);