1 files changed, 294 insertions, 0 deletions
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
new file mode 100644
index 0000000000..9073430dc8
--- /dev/null
+++ b/lib/percpu_counter.c
@@ -0,0 +1,294 @@
+// 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_many(struct percpu_counter *fbc, s64 amount,
+			       gfp_t gfp, u32 nr_counters,
+			       struct lock_class_key *key)
+{
+	unsigned long flags __maybe_unused;
+	size_t counter_size;
+	s32 __percpu *counters;
+	u32 i;
+
+	counter_size = ALIGN(sizeof(*counters), __alignof__(*counters));
+	counters = __alloc_percpu_gfp(nr_counters * counter_size,
+				      __alignof__(*counters), gfp);
+	if (!counters) {
+		fbc[0].counters = NULL;
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < nr_counters; i++) {
+		raw_spin_lock_init(&fbc[i].lock);
+		lockdep_set_class(&fbc[i].lock, key);
+#ifdef CONFIG_HOTPLUG_CPU
+		INIT_LIST_HEAD(&fbc[i].list);
+#endif
+		fbc[i].count = amount;
+		fbc[i].counters = (void *)counters + (i * counter_size);
+
+		debug_percpu_counter_activate(&fbc[i]);
+	}
+
+#ifdef CONFIG_HOTPLUG_CPU
+	spin_lock_irqsave(&percpu_counters_lock, flags);
+	for (i = 0; i < nr_counters; i++)
+		list_add(&fbc[i].list, &percpu_counters);
+	spin_unlock_irqrestore(&percpu_counters_lock, flags);
+#endif
+	return 0;
+}
+EXPORT_SYMBOL(__percpu_counter_init_many);
+
+void percpu_counter_destroy_many(struct percpu_counter *fbc, u32 nr_counters)
+{
+	unsigned long flags __maybe_unused;
+	u32 i;
+
+	if (WARN_ON_ONCE(!fbc))
+		return;
+
+	if (!fbc[0].counters)
+		return;
+
+	for (i = 0; i < nr_counters; i++)
+		debug_percpu_counter_deactivate(&fbc[i]);
+
+#ifdef CONFIG_HOTPLUG_CPU
+	spin_lock_irqsave(&percpu_counters_lock, flags);
+	for (i = 0; i < nr_counters; i++)
+		list_del(&fbc[i].list);
+	spin_unlock_irqrestore(&percpu_counters_lock, flags);
+#endif
+
+	free_percpu(fbc[0].counters);
+
+	for (i = 0; i < nr_counters; i++)
+		fbc[i].counters = NULL;
+}
+EXPORT_SYMBOL(percpu_counter_destroy_many);
+
+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);