1 files changed, 83 insertions, 0 deletions
diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
new file mode 100644
index 00000000000..250a4acddb2
--- /dev/null
+++ b/include/linux/percpu-rwsem.h
@@ -0,0 +1,83 @@
+#ifndef _LINUX_PERCPU_RWSEM_H
+#define _LINUX_PERCPU_RWSEM_H
+
+#include <linux/mutex.h>
+#include <linux/percpu.h>
+#include <linux/rcupdate.h>
+#include <linux/delay.h>
+
+struct percpu_rw_semaphore {
+	unsigned __percpu *counters;
+	bool locked;
+	struct mutex mtx;
+};
+
+#define light_mb()	barrier()
+#define heavy_mb()	synchronize_sched()
+
+static inline void percpu_down_read(struct percpu_rw_semaphore *p)
+{
+	rcu_read_lock_sched();
+	if (unlikely(p->locked)) {
+		rcu_read_unlock_sched();
+		mutex_lock(&p->mtx);
+		this_cpu_inc(*p->counters);
+		mutex_unlock(&p->mtx);
+		return;
+	}
+	this_cpu_inc(*p->counters);
+	rcu_read_unlock_sched();
+	light_mb(); /* A, between read of p->locked and read of data, paired with D */
+}
+
+static inline void percpu_up_read(struct percpu_rw_semaphore *p)
+{
+	light_mb(); /* B, between read of the data and write to p->counter, paired with C */
+	this_cpu_dec(*p->counters);
+}
+
+static inline unsigned __percpu_count(unsigned __percpu *counters)
+{
+	unsigned total = 0;
+	int cpu;
+
+	for_each_possible_cpu(cpu)
+		total += ACCESS_ONCE(*per_cpu_ptr(counters, cpu));
+
+	return total;
+}
+
+static inline void percpu_down_write(struct percpu_rw_semaphore *p)
+{
+	mutex_lock(&p->mtx);
+	p->locked = true;
+	synchronize_sched(); /* make sure that all readers exit the rcu_read_lock_sched region */
+	while (__percpu_count(p->counters))
+		msleep(1);
+	heavy_mb(); /* C, between read of p->counter and write to data, paired with B */
+}
+
+static inline void percpu_up_write(struct percpu_rw_semaphore *p)
+{
+	heavy_mb(); /* D, between write to data and write to p->locked, paired with A */
+	p->locked = false;
+	mutex_unlock(&p->mtx);
+}
+
+static inline int percpu_init_rwsem(struct percpu_rw_semaphore *p)
+{
+	p->counters = alloc_percpu(unsigned);
+	if (unlikely(!p->counters))
+		return -ENOMEM;
+	p->locked = false;
+	mutex_init(&p->mtx);
+	return 0;
+}
+
+static inline void percpu_free_rwsem(struct percpu_rw_semaphore *p)
+{
+	free_percpu(p->counters);
+	p->counters = NULL; /* catch use after free bugs */
+}
+
+#endif