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Commit 3a101d05 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarPeter 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>
parent 50a323b7

include/linux/cpu.h

+16 −0
Original line number Diff line number Diff line
@@ -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,

include/linux/cpuset.h

+6 −0
Original line number Diff line number Diff line
@@ -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)

{

kernel/cpu.c

+0 −6
Original line number Diff line number Diff line
@@ -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);

kernel/cpuset.c

+2 −19
Original line number Diff line number Diff line
@@ -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");

kernel/sched.c

+50 −17
Original line number Diff line number Diff line
@@ -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,

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);