Release 4.15 kernel/cpu.c

/* CPU control.
 * (C) 2001, 2002, 2003, 2004 Rusty Russell
 *
 * This code is licenced under the GPL.
 */
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched/signal.h>
#include <linux/sched/hotplug.h>
#include <linux/sched/task.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/rcupdate.h>
#include <linux/export.h>
#include <linux/bug.h>
#include <linux/kthread.h>
#include <linux/stop_machine.h>
#include <linux/mutex.h>
#include <linux/gfp.h>
#include <linux/suspend.h>
#include <linux/lockdep.h>
#include <linux/tick.h>
#include <linux/irq.h>
#include <linux/nmi.h>
#include <linux/smpboot.h>
#include <linux/relay.h>
#include <linux/slab.h>
#include <linux/percpu-rwsem.h>

#include <trace/events/power.h>

#define CREATE_TRACE_POINTS
#include <trace/events/cpuhp.h>

#include "smpboot.h"

/**
 * cpuhp_cpu_state - Per cpu hotplug state storage
 * @state:      The current cpu state
 * @target:     The target state
 * @thread:     Pointer to the hotplug thread
 * @should_run: Thread should execute
 * @rollback:   Perform a rollback
 * @single:     Single callback invocation
 * @bringup:    Single callback bringup or teardown selector
 * @cb_state:   The state for a single callback (install/uninstall)
 * @result:     Result of the operation
 * @done_up:    Signal completion to the issuer of the task for cpu-up
 * @done_down:  Signal completion to the issuer of the task for cpu-down
 */

struct cpuhp_cpu_state {
	
enum cpuhp_state	state;
	
enum cpuhp_state	target;
	
enum cpuhp_state	fail;
#ifdef CONFIG_SMP
	
struct task_struct	*thread;
	
bool			should_run;
	
bool			rollback;
	
bool			single;
	
bool			bringup;
	
struct hlist_node	*node;
	
struct hlist_node	*last;
	
enum cpuhp_state	cb_state;
	
int			result;
	
struct completion	done_up;
	
struct completion	done_down;
#endif
};

static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
	.fail = CPUHP_INVALID,
};

#if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)

static struct lockdep_map cpuhp_state_up_map =
	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);

static struct lockdep_map cpuhp_state_down_map =
	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);




static inline void cpuhp_lock_acquire(bool bringup)
{
	lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
}

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static inline void cpuhp_lock_release(bool bringup)
{
	lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
}
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#else



static inline void cpuhp_lock_acquire(bool bringup) { }
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static inline void cpuhp_lock_release(bool bringup) { }

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#endif

/**
 * cpuhp_step - Hotplug state machine step
 * @name:       Name of the step
 * @startup:    Startup function of the step
 * @teardown:   Teardown function of the step
 * @skip_onerr: Do not invoke the functions on error rollback
 *              Will go away once the notifiers are gone
 * @cant_stop:  Bringup/teardown can't be stopped at this step
 */

struct cpuhp_step {
	
const char		*name;
	union {
		
int		(*single)(unsigned int cpu);
		
int		(*multi)(unsigned int cpu,
					 struct hlist_node *node);
	
} startup;
	union {
		
int		(*single)(unsigned int cpu);
		
int		(*multi)(unsigned int cpu,
					 struct hlist_node *node);
	
} teardown;
	
struct hlist_head	list;
	
bool			skip_onerr;
	
bool			cant_stop;
	
bool			multi_instance;
};

static DEFINE_MUTEX(cpuhp_state_mutex);

static struct cpuhp_step cpuhp_bp_states[];

static struct cpuhp_step cpuhp_ap_states[];



static bool cpuhp_is_ap_state(enum cpuhp_state state)
{
	/*
         * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
         * purposes as that state is handled explicitly in cpu_down.
         */
	return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
}

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static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
{
	struct cpuhp_step *sp;

	sp = cpuhp_is_ap_state(state) ? cpuhp_ap_states : cpuhp_bp_states;
	return sp + state;
}

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/**
 * cpuhp_invoke_callback _ Invoke the callbacks for a given state
 * @cpu:        The cpu for which the callback should be invoked
 * @state:      The state to do callbacks for
 * @bringup:    True if the bringup callback should be invoked
 * @node:       For multi-instance, do a single entry callback for install/remove
 * @lastp:      For multi-instance rollback, remember how far we got
 *
 * Called from cpu hotplug and from the state register machinery.
 */


static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
				 bool bringup, struct hlist_node *node,
				 struct hlist_node **lastp)
{
	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
	struct cpuhp_step *step = cpuhp_get_step(state);
	int (*cbm)(unsigned int cpu, struct hlist_node *node);
	int (*cb)(unsigned int cpu);
	int ret, cnt;

	if (st->fail == state) {
		st->fail = CPUHP_INVALID;

		if (!(bringup ? step->startup.single : step->teardown.single))
			return 0;

		return -EAGAIN;
	}

	if (!step->multi_instance) {
		WARN_ON_ONCE(lastp && *lastp);
		cb = bringup ? step->startup.single : step->teardown.single;
		if (!cb)
			return 0;
		trace_cpuhp_enter(cpu, st->target, state, cb);
		ret = cb(cpu);
		trace_cpuhp_exit(cpu, st->state, state, ret);
		return ret;
	}
	cbm = bringup ? step->startup.multi : step->teardown.multi;
	if (!cbm)
		return 0;

	/* Single invocation for instance add/remove */
	if (node) {
		WARN_ON_ONCE(lastp && *lastp);
		trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
		ret = cbm(cpu, node);
		trace_cpuhp_exit(cpu, st->state, state, ret);
		return ret;
	}

	/* State transition. Invoke on all instances */
	cnt = 0;
	hlist_for_each(node, &step->list) {
		if (lastp && node == *lastp)
			break;

		trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
		ret = cbm(cpu, node);
		trace_cpuhp_exit(cpu, st->state, state, ret);
		if (ret) {
			if (!lastp)
				goto err;

			*lastp = node;
			return ret;
		}
		cnt++;
	}
	if (lastp)
		*lastp = NULL;
	return 0;
err:
	/* Rollback the instances if one failed */
	cbm = !bringup ? step->startup.multi : step->teardown.multi;
	if (!cbm)
		return ret;

	hlist_for_each(node, &step->list) {
		if (!cnt--)
			break;

		trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
		ret = cbm(cpu, node);
		trace_cpuhp_exit(cpu, st->state, state, ret);
		/*
                 * Rollback must not fail,
                 */
		WARN_ON_ONCE(ret);
	}
	return ret;
}

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#ifdef CONFIG_SMP


static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
{
	struct completion *done = bringup ? &st->done_up : &st->done_down;
	wait_for_completion(done);
}

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static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
{
	struct completion *done = bringup ? &st->done_up : &st->done_down;
	complete(done);
}

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/*
 * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
 */


static bool cpuhp_is_atomic_state(enum cpuhp_state state)
{
	return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
}

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/* Serializes the updates to cpu_online_mask, cpu_present_mask */
static DEFINE_MUTEX(cpu_add_remove_lock);

bool cpuhp_tasks_frozen;

EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);

/*
 * The following two APIs (cpu_maps_update_begin/done) must be used when
 * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
 */


void cpu_maps_update_begin(void)
{
	mutex_lock(&cpu_add_remove_lock);
}

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void cpu_maps_update_done(void)
{
	mutex_unlock(&cpu_add_remove_lock);
}

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/*
 * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
 * Should always be manipulated under cpu_add_remove_lock
 */

static int cpu_hotplug_disabled;

#ifdef CONFIG_HOTPLUG_CPU


DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);



void cpus_read_lock(void)
{
	percpu_down_read(&cpu_hotplug_lock);
}
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EXPORT_SYMBOL_GPL(cpus_read_lock);



void cpus_read_unlock(void)
{
	percpu_up_read(&cpu_hotplug_lock);
}
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EXPORT_SYMBOL_GPL(cpus_read_unlock);



void cpus_write_lock(void)
{
	percpu_down_write(&cpu_hotplug_lock);
}

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void cpus_write_unlock(void)
{
	percpu_up_write(&cpu_hotplug_lock);
}

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void lockdep_assert_cpus_held(void)
{
	percpu_rwsem_assert_held(&cpu_hotplug_lock);
}

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/*
 * Wait for currently running CPU hotplug operations to complete (if any) and
 * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
 * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
 * hotplug path before performing hotplug operations. So acquiring that lock
 * guarantees mutual exclusion from any currently running hotplug operations.
 */


void cpu_hotplug_disable(void)
{
	cpu_maps_update_begin();
	cpu_hotplug_disabled++;
	cpu_maps_update_done();
}
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EXPORT_SYMBOL_GPL(cpu_hotplug_disable);



static void __cpu_hotplug_enable(void)
{
	if (WARN_ONCE(!cpu_hotplug_disabled, "Unbalanced cpu hotplug enable\n"))
		return;
	cpu_hotplug_disabled--;
}

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void cpu_hotplug_enable(void)
{
	cpu_maps_update_begin();
	__cpu_hotplug_enable();
	cpu_maps_update_done();
}
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EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
#endif	/* CONFIG_HOTPLUG_CPU */


static inline enum cpuhp_state

cpuhp_set_state(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
	enum cpuhp_state prev_state = st->state;

	st->rollback = false;
	st->last = NULL;

	st->target = target;
	st->single = false;
	st->bringup = st->state < target;

	return prev_state;
}

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static inline void

cpuhp_reset_state(struct cpuhp_cpu_state *st, enum cpuhp_state prev_state)
{
	st->rollback = true;

	/*
         * If we have st->last we need to undo partial multi_instance of this
         * state first. Otherwise start undo at the previous state.
         */
	if (!st->last) {
		if (st->bringup)
			st->state--;
		else
			st->state++;
	}

	st->target = prev_state;
	st->bringup = !st->bringup;
}

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/* Regular hotplug invocation of the AP hotplug thread */


static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
{
	if (!st->single && st->state == st->target)
		return;

	st->result = 0;
	/*
         * Make sure the above stores are visible before should_run becomes
         * true. Paired with the mb() above in cpuhp_thread_fun()
         */
	smp_mb();
	st->should_run = true;
	wake_up_process(st->thread);
	wait_for_ap_thread(st, st->bringup);
}

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static int cpuhp_kick_ap(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
	enum cpuhp_state prev_state;
	int ret;

	prev_state = cpuhp_set_state(st, target);
	__cpuhp_kick_ap(st);
	if ((ret = st->result)) {
		cpuhp_reset_state(st, prev_state);
		__cpuhp_kick_ap(st);
	}

	return ret;
}

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static int bringup_wait_for_ap(unsigned int cpu)
{
	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

	/* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
	wait_for_ap_thread(st, true);
	if (WARN_ON_ONCE((!cpu_online(cpu))))
		return -ECANCELED;

	/* Unpark the stopper thread and the hotplug thread of the target cpu */
	stop_machine_unpark(cpu);
	kthread_unpark(st->thread);

	if (st->target <= CPUHP_AP_ONLINE_IDLE)
		return 0;

	return cpuhp_kick_ap(st, st->target);
}

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static int bringup_cpu(unsigned int cpu)
{
	struct task_struct *idle = idle_thread_get(cpu);
	int ret;

	/*
         * Some architectures have to walk the irq descriptors to
         * setup the vector space for the cpu which comes online.
         * Prevent irq alloc/free across the bringup.
         */
	irq_lock_sparse();

	/* Arch-specific enabling code. */
	ret = __cpu_up(cpu, idle);
	irq_unlock_sparse();
	if (ret)
		return ret;
	return bringup_wait_for_ap(cpu);
}

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/*
 * Hotplug state machine related functions
 */



static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
{
	for (st->state--; st->state > st->target; st->state--) {
		struct cpuhp_step *step = cpuhp_get_step(st->state);

		if (!step->skip_onerr)
			cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
	}
}

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static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
			      enum cpuhp_state target)
{
	enum cpuhp_state prev_state = st->state;
	int ret = 0;

	while (st->state < target) {
		st->state++;
		ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
		if (ret) {
			st->target = prev_state;
			undo_cpu_up(cpu, st);
			break;
		}
	}
	return ret;
}

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/*
 * The cpu hotplug threads manage the bringup and teardown of the cpus
 */


static void cpuhp_create(unsigned int cpu)
{
	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

	init_completion(&st->done_up);
	init_completion(&st->done_down);
}

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static int cpuhp_should_run(unsigned int cpu)
{
	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

	return st->should_run;
}

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/*
 * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
 * callbacks when a state gets [un]installed at runtime.
 *
 * Each invocation of this function by the smpboot thread does a single AP
 * state callback.
 *
 * It has 3 modes of operation:
 *  - single: runs st->cb_state
 *  - up:     runs ++st->state, while st->state < st->target
 *  - down:   runs st->state--, while st->state > st->target
 *
 * When complete or on error, should_run is cleared and the completion is fired.
 */


static void cpuhp_thread_fun(unsigned int cpu)
{
	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
	bool bringup = st->bringup;
	enum cpuhp_state state;

	/*
         * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
         * that if we see ->should_run we also see the rest of the state.
         */
	smp_mb();

	if (WARN_ON_ONCE(!st->should_run))
		return;

	cpuhp_lock_acquire(bringup);

	if (st->single) {
		state = st->cb_state;
		st->should_run = false;
	} else {
		if (bringup) {
			st->state++;
			state = st->state;
			st->should_run = (st->state < st->target);
			WARN_ON_ONCE(st->state > st->target);
		} else {
			state = st->state;
			st->state--;
			st->should_run = (st->state > st->target);
			WARN_ON_ONCE(st->state < st->target);
		}
	}

	WARN_ON_ONCE(!cpuhp_is_ap_state(state));

	if (st->rollback) {
		struct cpuhp_step *step = cpuhp_get_step(state);
		if (step->skip_onerr)
			goto next;
	}

	if (cpuhp_is_atomic_state(state)) {
		local_irq_disable();
		st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
		local_irq_enable();

		/*
                 * STARTING/DYING must not fail!
                 */
		WARN_ON_ONCE(st->result);
	} else {
		st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
	}

	if (st->result) {
		/*
                 * If we fail on a rollback, we're up a creek without no
                 * paddle, no way forward, no way back. We loose, thanks for
                 * playing.
                 */
		WARN_ON_ONCE(st->rollback);
		st->should_run = false;
	}

next:
	cpuhp_lock_release(bringup);

	if (!st->should_run)
		complete_ap_thread(st, bringup);
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Peter Zijlstra
185
60.66%
3
33.33%
Thomas Gleixner
101
33.11%
5
55.56%
Sebastian Andrzej Siewior
19
6.23%
1
11.11%
Total
305
100.00%
9
100.00%

/* Invoke a single callback on a remote cpu */

static int

cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
			 struct hlist_node *node)
{
	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
	int ret;

	if (!cpu_online(cpu))
		return 0;

	cpuhp_lock_acquire(false);
	cpuhp_lock_release(false);

	cpuhp_lock_acquire(true);
	cpuhp_lock_release(true);

	/*
         * If we are up and running, use the hotplug thread. For early calls
         * we invoke the thread function directly.
         */
	if (!st->thread)
		return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);

	st->rollback = false;
	st->last = NULL;

	st->node = node;
	st->bringup = bringup;
	st->cb_state = state;
	st->single = true;

	__cpuhp_kick_ap(st);

	/*
         * If we failed and did a partial, do a rollback.
         */
	if ((ret = st->result) && st->last) {
		st->rollback = true;
		st->bringup = !bringup;

		__cpuhp_kick_ap(st);
	}

	/*
         * Clean up the leftovers so the next hotplug operation wont use stale
         * data.
         */
	st->node = st->last = NULL;
	return ret;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Thomas Gleixner
126
70.00%
8
72.73%
Peter Zijlstra
54
30.00%
3
27.27%
Total
180
100.00%
11
100.00%



static int cpuhp_kick_ap_work(unsigned int cpu)
{
	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
	enum cpuhp_state prev_state = st->state;
	int ret;

	cpuhp_lock_acquire(false);
	cpuhp_lock_release(false);

	cpuhp_lock_acquire(true);
	cpuhp_lock_release(true);

	trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
	ret = cpuhp_kick_ap(st, st->target);
	trace_cpuhp_exit(cpu, st->state, prev_state, ret);

	return ret;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Thomas Gleixner
58
61.70%
3
60.00%
Peter Zijlstra
36
38.30%
2
40.00%
Total
94
100.00%
5
100.00%


static struct smp_hotplug_thread cpuhp_threads = {
	.store			= &cpuhp_state.thread,
	.create			= &cpuhp_create,
	.thread_should_run	= cpuhp_should_run,
	.thread_fn		= cpuhp_thread_fun,
	.thread_comm		= "cpuhp/%u",
	.selfparking		= true,
};



void __init cpuhp_threads_init(void)
{
	BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
	kthread_unpark(this_cpu_read(cpuhp_state.thread));
}

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Thomas Gleixner
27
100.00%
1
100.00%
Total
27
100.00%
1
100.00%

#ifdef CONFIG_HOTPLUG_CPU
/**
 * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
 * @cpu: a CPU id
 *
 * This function walks all processes, finds a valid mm struct for each one and
 * then clears a corresponding bit in mm's cpumask.  While this all sounds
 * trivial, there are various non-obvious corner cases, which this function
 * tries to solve in a safe manner.
 *
 * Also note that the function uses a somewhat relaxed locking scheme, so it may
 * be called only for an already offlined CPU.
 */


void clear_tasks_mm_cpumask(int cpu)
{
	struct task_struct *p;

	/*
         * This function is called after the cpu is taken down and marked
         * offline, so its not like new tasks will ever get this cpu set in
         * their mm mask. -- Peter Zijlstra
         * Thus, we may use rcu_read_lock() here, instead of grabbing
         * full-fledged tasklist_lock.
         */
	WARN_ON(cpu_online(cpu));
	rcu_read_lock();
	for_each_process(p) {
		struct task_struct *t;

		/*
                 * Main thread might exit, but other threads may still have
                 * a valid mm. Find one.
                 */
		t = find_lock_task_mm(p);
		if (!t)
			continue;
		cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
		task_unlock(t);
	}
	rcu_read_unlock();
}

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Anton Vorontsov
70
100.00%
2
100.00%
Total
70
100.00%
2
100.00%

/* Take this CPU down. */


static int take_cpu_down(void *_param)
{
	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
	int err, cpu = smp_processor_id();
	int ret;

	/* Ensure this CPU doesn't handle any more interrupts. */
	err = __cpu_disable();
	if (err < 0)
		return err;

	/*
         * We get here while we are in CPUHP_TEARDOWN_CPU state and we must not
         * do this step again.
         */
	WARN_ON(st->state != CPUHP_TEARDOWN_CPU);
	st->state--;
	/* Invoke the former CPU_DYING callbacks */
	for (; st->state > target; st->state--) {
		ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
		/*
                 * DYING must not fail!
                 */
		WARN_ON_ONCE(ret);
	}

	/* Give up timekeeping duties */
	tick_handover_do_timer();
	/* Park the stopper thread */
	stop_machine_park(cpu);
	return 0;
}

Contributors
Person
Tokens
Prop
Commits
CommitProp
Thomas Gleixner
116
88.55%
4
66.67%
Peter Zijlstra
15
11.45%
2
33.33%
Total
131
100.00%
6
100.00%



static int takedown_cpu(unsigned int cpu)
{
	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
	int err;

	/* Park the smpboot threads */
	kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);
	smpboot_park_threads(cpu);

	/*
         * Prevent irq alloc/free while the dying cpu reorganizes the
         * interrupt affinities.
         */
	irq_lock_sparse();