lib/percpu_counter.c - third_party/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Fast batching percpu counters.
  */

 #include <linux/percpu_counter.h>
 #include <linux/mutex.h>
 #include <linux/init.h>
 #include <linux/cpu.h>
 #include <linux/module.h>
 #include <linux/debugobjects.h>

 #ifdef CONFIG_HOTPLUG_CPU
 static LIST_HEAD(percpu_counters);
 static DEFINE_SPINLOCK(percpu_counters_lock);
 #endif

 #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER

 static const struct debug_obj_descr percpu_counter_debug_descr;

 static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
 {
 	struct percpu_counter *fbc = addr;

 	switch (state) {
 	case ODEBUG_STATE_ACTIVE:
 		percpu_counter_destroy(fbc);
 		debug_object_free(fbc, &percpu_counter_debug_descr);
 		return true;
 	default:
 		return false;
 	}
 }

 static const struct debug_obj_descr percpu_counter_debug_descr = {
 	.name		= "percpu_counter",
 	.fixup_free	= percpu_counter_fixup_free,
 };

 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
 {
 	debug_object_init(fbc, &percpu_counter_debug_descr);
 	debug_object_activate(fbc, &percpu_counter_debug_descr);
 }

 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
 {
 	debug_object_deactivate(fbc, &percpu_counter_debug_descr);
 	debug_object_free(fbc, &percpu_counter_debug_descr);
 }

 #else	/* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
 { }
 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
 { }
 #endif	/* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */

 void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
 {
 	int cpu;
 	unsigned long flags;

 	raw_spin_lock_irqsave(&fbc->lock, flags);
 	for_each_possible_cpu(cpu) {
 		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
 		*pcount = 0;
 	}
 	fbc->count = amount;
 	raw_spin_unlock_irqrestore(&fbc->lock, flags);
 }
 EXPORT_SYMBOL(percpu_counter_set);

 /*
  * local_irq_save() is needed to make the function irq safe:
  * - The slow path would be ok as protected by an irq-safe spinlock.
  * - this_cpu_add would be ok as it is irq-safe by definition.
  * But:
  * The decision slow path/fast path and the actual update must be atomic, too.
  * Otherwise a call in process context could check the current values and
  * decide that the fast path can be used. If now an interrupt occurs before
  * the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters),
  * then the this_cpu_add() that is executed after the interrupt has completed
  * can produce values larger than "batch" or even overflows.
  */
 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
 {
 	s64 count;
 	unsigned long flags;

 	local_irq_save(flags);
 	count = __this_cpu_read(*fbc->counters) + amount;
 	if (abs(count) >= batch) {
 		raw_spin_lock(&fbc->lock);
 		fbc->count += count;
 		__this_cpu_sub(*fbc->counters, count - amount);
 		raw_spin_unlock(&fbc->lock);
 	} else {
 		this_cpu_add(*fbc->counters, amount);
 	}
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL(percpu_counter_add_batch);

 /*
  * For percpu_counter with a big batch, the devication of its count could
  * be big, and there is requirement to reduce the deviation, like when the
  * counter's batch could be runtime decreased to get a better accuracy,
  * which can be achieved by running this sync function on each CPU.
  */
 void percpu_counter_sync(struct percpu_counter *fbc)
 {
 	unsigned long flags;
 	s64 count;

 	raw_spin_lock_irqsave(&fbc->lock, flags);
 	count = __this_cpu_read(*fbc->counters);
 	fbc->count += count;
 	__this_cpu_sub(*fbc->counters, count);
 	raw_spin_unlock_irqrestore(&fbc->lock, flags);
 }
 EXPORT_SYMBOL(percpu_counter_sync);

 /*
  * Add up all the per-cpu counts, return the result.  This is a more accurate
  * but much slower version of percpu_counter_read_positive().
  *
  * We use the cpu mask of (cpu_online_mask | cpu_dying_mask) to capture sums
  * from CPUs that are in the process of being taken offline. Dying cpus have
  * been removed from the online mask, but may not have had the hotplug dead
  * notifier called to fold the percpu count back into the global counter sum.
  * By including dying CPUs in the iteration mask, we avoid this race condition
  * so __percpu_counter_sum() just does the right thing when CPUs are being taken
  * offline.
  */
 s64 __percpu_counter_sum(struct percpu_counter *fbc)
 {
 	s64 ret;
 	int cpu;
 	unsigned long flags;

 	raw_spin_lock_irqsave(&fbc->lock, flags);
 	ret = fbc->count;
 	for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
 		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
 		ret += *pcount;
 	}
 	raw_spin_unlock_irqrestore(&fbc->lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL(__percpu_counter_sum);

 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
 			  struct lock_class_key *key)
 {
 	unsigned long flags __maybe_unused;

 	raw_spin_lock_init(&fbc->lock);
 	lockdep_set_class(&fbc->lock, key);
 	fbc->count = amount;
 	fbc->counters = alloc_percpu_gfp(s32, gfp);
 	if (!fbc->counters)
 		return -ENOMEM;

 	debug_percpu_counter_activate(fbc);

 #ifdef CONFIG_HOTPLUG_CPU
 	INIT_LIST_HEAD(&fbc->list);
 	spin_lock_irqsave(&percpu_counters_lock, flags);
 	list_add(&fbc->list, &percpu_counters);
 	spin_unlock_irqrestore(&percpu_counters_lock, flags);
 #endif
 	return 0;
 }
 EXPORT_SYMBOL(__percpu_counter_init);

 void percpu_counter_destroy(struct percpu_counter *fbc)
 {
 	unsigned long flags __maybe_unused;

 	if (!fbc->counters)
 		return;

 	debug_percpu_counter_deactivate(fbc);

 #ifdef CONFIG_HOTPLUG_CPU
 	spin_lock_irqsave(&percpu_counters_lock, flags);
 	list_del(&fbc->list);
 	spin_unlock_irqrestore(&percpu_counters_lock, flags);
 #endif
 	free_percpu(fbc->counters);
 	fbc->counters = NULL;
 }
 EXPORT_SYMBOL(percpu_counter_destroy);

 int percpu_counter_batch __read_mostly = 32;
 EXPORT_SYMBOL(percpu_counter_batch);

 static int compute_batch_value(unsigned int cpu)
 {
 	int nr = num_online_cpus();

 	percpu_counter_batch = max(32, nr*2);
 	return 0;
 }

 static int percpu_counter_cpu_dead(unsigned int cpu)
 {
 #ifdef CONFIG_HOTPLUG_CPU
 	struct percpu_counter *fbc;

 	compute_batch_value(cpu);

 	spin_lock_irq(&percpu_counters_lock);
 	list_for_each_entry(fbc, &percpu_counters, list) {
 		s32 *pcount;

 		raw_spin_lock(&fbc->lock);
 		pcount = per_cpu_ptr(fbc->counters, cpu);
 		fbc->count += *pcount;
 		*pcount = 0;
 		raw_spin_unlock(&fbc->lock);
 	}
 	spin_unlock_irq(&percpu_counters_lock);
 #endif
 	return 0;
 }

 /*
  * Compare counter against given value.
  * Return 1 if greater, 0 if equal and -1 if less
  */
 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
 {
 	s64	count;

 	count = percpu_counter_read(fbc);
 	/* Check to see if rough count will be sufficient for comparison */
 	if (abs(count - rhs) > (batch * num_online_cpus())) {
 		if (count > rhs)
 			return 1;
 		else
 			return -1;
 	}
 	/* Need to use precise count */
 	count = percpu_counter_sum(fbc);
 	if (count > rhs)
 		return 1;
 	else if (count < rhs)
 		return -1;
 	else
 		return 0;
 }
 EXPORT_SYMBOL(__percpu_counter_compare);

 static int __init percpu_counter_startup(void)
 {
 	int ret;

 	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
 				compute_batch_value, NULL);
 	WARN_ON(ret < 0);
 	ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
 					"lib/percpu_cnt:dead", NULL,
 					percpu_counter_cpu_dead);
 	WARN_ON(ret < 0);
 	return 0;
 }
 module_init(percpu_counter_startup);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Fast batching percpu counters.
	*/

	#include <linux/percpu_counter.h>
	#include <linux/mutex.h>
	#include <linux/init.h>
	#include <linux/cpu.h>
	#include <linux/module.h>
	#include <linux/debugobjects.h>

	#ifdef CONFIG_HOTPLUG_CPU
	static LIST_HEAD(percpu_counters);
	static DEFINE_SPINLOCK(percpu_counters_lock);
	#endif

	#ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER

	static const struct debug_obj_descr percpu_counter_debug_descr;

	static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
	{
	struct percpu_counter *fbc = addr;

	switch (state) {
	case ODEBUG_STATE_ACTIVE:
	percpu_counter_destroy(fbc);
	debug_object_free(fbc, &percpu_counter_debug_descr);
	return true;
	default:
	return false;
	}
	}

	static const struct debug_obj_descr percpu_counter_debug_descr = {
	.name = "percpu_counter",
	.fixup_free = percpu_counter_fixup_free,
	};

	static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
	{
	debug_object_init(fbc, &percpu_counter_debug_descr);
	debug_object_activate(fbc, &percpu_counter_debug_descr);
	}

	static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
	{
	debug_object_deactivate(fbc, &percpu_counter_debug_descr);
	debug_object_free(fbc, &percpu_counter_debug_descr);
	}

	#else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
	static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
	{ }
	static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
	{ }
	#endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */

	void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
	{
	int cpu;
	unsigned long flags;

	raw_spin_lock_irqsave(&fbc->lock, flags);
	for_each_possible_cpu(cpu) {
	s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
	*pcount = 0;
	}
	fbc->count = amount;
	raw_spin_unlock_irqrestore(&fbc->lock, flags);
	}
	EXPORT_SYMBOL(percpu_counter_set);

	/*
	* local_irq_save() is needed to make the function irq safe:
	* - The slow path would be ok as protected by an irq-safe spinlock.
	* - this_cpu_add would be ok as it is irq-safe by definition.
	* But:
	* The decision slow path/fast path and the actual update must be atomic, too.
	* Otherwise a call in process context could check the current values and
	* decide that the fast path can be used. If now an interrupt occurs before
	* the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters),
	* then the this_cpu_add() that is executed after the interrupt has completed
	* can produce values larger than "batch" or even overflows.
	*/
	void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
	{
	s64 count;
	unsigned long flags;

	local_irq_save(flags);
	count = __this_cpu_read(*fbc->counters) + amount;
	if (abs(count) >= batch) {
	raw_spin_lock(&fbc->lock);
	fbc->count += count;
	__this_cpu_sub(*fbc->counters, count - amount);
	raw_spin_unlock(&fbc->lock);
	} else {
	this_cpu_add(*fbc->counters, amount);
	}
	local_irq_restore(flags);
	}
	EXPORT_SYMBOL(percpu_counter_add_batch);

	/*
	* For percpu_counter with a big batch, the devication of its count could
	* be big, and there is requirement to reduce the deviation, like when the
	* counter's batch could be runtime decreased to get a better accuracy,
	* which can be achieved by running this sync function on each CPU.
	*/
	void percpu_counter_sync(struct percpu_counter *fbc)
	{
	unsigned long flags;
	s64 count;

	raw_spin_lock_irqsave(&fbc->lock, flags);
	count = __this_cpu_read(*fbc->counters);
	fbc->count += count;
	__this_cpu_sub(*fbc->counters, count);
	raw_spin_unlock_irqrestore(&fbc->lock, flags);
	}
	EXPORT_SYMBOL(percpu_counter_sync);

	/*
	* Add up all the per-cpu counts, return the result. This is a more accurate
	* but much slower version of percpu_counter_read_positive().
	*
	* We use the cpu mask of (cpu_online_mask \| cpu_dying_mask) to capture sums
	* from CPUs that are in the process of being taken offline. Dying cpus have
	* been removed from the online mask, but may not have had the hotplug dead
	* notifier called to fold the percpu count back into the global counter sum.
	* By including dying CPUs in the iteration mask, we avoid this race condition
	* so __percpu_counter_sum() just does the right thing when CPUs are being taken
	* offline.
	*/
	s64 __percpu_counter_sum(struct percpu_counter *fbc)
	{
	s64 ret;
	int cpu;
	unsigned long flags;

	raw_spin_lock_irqsave(&fbc->lock, flags);
	ret = fbc->count;
	for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
	s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
	ret += *pcount;
	}
	raw_spin_unlock_irqrestore(&fbc->lock, flags);
	return ret;
	}
	EXPORT_SYMBOL(__percpu_counter_sum);

	int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
	struct lock_class_key *key)
	{
	unsigned long flags __maybe_unused;

	raw_spin_lock_init(&fbc->lock);
	lockdep_set_class(&fbc->lock, key);
	fbc->count = amount;
	fbc->counters = alloc_percpu_gfp(s32, gfp);
	if (!fbc->counters)
	return -ENOMEM;

	debug_percpu_counter_activate(fbc);

	#ifdef CONFIG_HOTPLUG_CPU
	INIT_LIST_HEAD(&fbc->list);
	spin_lock_irqsave(&percpu_counters_lock, flags);
	list_add(&fbc->list, &percpu_counters);
	spin_unlock_irqrestore(&percpu_counters_lock, flags);
	#endif
	return 0;
	}
	EXPORT_SYMBOL(__percpu_counter_init);

	void percpu_counter_destroy(struct percpu_counter *fbc)
	{
	unsigned long flags __maybe_unused;

	if (!fbc->counters)
	return;

	debug_percpu_counter_deactivate(fbc);

	#ifdef CONFIG_HOTPLUG_CPU
	spin_lock_irqsave(&percpu_counters_lock, flags);
	list_del(&fbc->list);
	spin_unlock_irqrestore(&percpu_counters_lock, flags);
	#endif
	free_percpu(fbc->counters);
	fbc->counters = NULL;
	}
	EXPORT_SYMBOL(percpu_counter_destroy);

	int percpu_counter_batch __read_mostly = 32;
	EXPORT_SYMBOL(percpu_counter_batch);

	static int compute_batch_value(unsigned int cpu)
	{
	int nr = num_online_cpus();

	percpu_counter_batch = max(32, nr*2);
	return 0;
	}

	static int percpu_counter_cpu_dead(unsigned int cpu)
	{
	#ifdef CONFIG_HOTPLUG_CPU
	struct percpu_counter *fbc;

	compute_batch_value(cpu);

	spin_lock_irq(&percpu_counters_lock);
	list_for_each_entry(fbc, &percpu_counters, list) {
	s32 *pcount;

	raw_spin_lock(&fbc->lock);
	pcount = per_cpu_ptr(fbc->counters, cpu);
	fbc->count += *pcount;
	*pcount = 0;
	raw_spin_unlock(&fbc->lock);
	}
	spin_unlock_irq(&percpu_counters_lock);
	#endif
	return 0;
	}

	/*
	* Compare counter against given value.
	* Return 1 if greater, 0 if equal and -1 if less
	*/
	int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
	{
	s64 count;

	count = percpu_counter_read(fbc);
	/* Check to see if rough count will be sufficient for comparison */
	if (abs(count - rhs) > (batch * num_online_cpus())) {
	if (count > rhs)
	return 1;
	else
	return -1;
	}
	/* Need to use precise count */
	count = percpu_counter_sum(fbc);
	if (count > rhs)
	return 1;
	else if (count < rhs)
	return -1;
	else
	return 0;
	}
	EXPORT_SYMBOL(__percpu_counter_compare);

	static int __init percpu_counter_startup(void)
	{
	int ret;

	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
	compute_batch_value, NULL);
	WARN_ON(ret < 0);
	ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
	"lib/percpu_cnt:dead", NULL,
	percpu_counter_cpu_dead);
	WARN_ON(ret < 0);
	return 0;
	}
	module_init(percpu_counter_startup);