1 files changed, 121 insertions, 0 deletions
diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
new file mode 100644
index 000000000000..146efefde2a1
--- /dev/null
+++ b/include/linux/percpu-rwsem.h
@@ -0,0 +1,121 @@
+#ifndef _LINUX_PERCPU_RWSEM_H
+#define _LINUX_PERCPU_RWSEM_H
+
+#include <linux/atomic.h>
+#include <linux/rwsem.h>
+#include <linux/percpu.h>
+#include <linux/wait.h>
+#include <linux/rcu_sync.h>
+#include <linux/lockdep.h>
+
+struct percpu_rw_semaphore {
+	struct rcu_sync		rss;
+	unsigned int __percpu	*read_count;
+	struct rw_semaphore	rw_sem;
+	wait_queue_head_t	writer;
+	int			readers_block;
+};
+
+extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
+extern void __percpu_up_read(struct percpu_rw_semaphore *);
+
+static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
+{
+	might_sleep();
+
+	rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
+
+	preempt_disable();
+	/*
+	 * We are in an RCU-sched read-side critical section, so the writer
+	 * cannot both change sem->state from readers_fast and start checking
+	 * counters while we are here. So if we see !sem->state, we know that
+	 * the writer won't be checking until we're past the preempt_enable()
+	 * and that one the synchronize_sched() is done, the writer will see
+	 * anything we did within this RCU-sched read-size critical section.
+	 */
+	__this_cpu_inc(*sem->read_count);
+	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
+		__percpu_down_read(sem, false); /* Unconditional memory barrier */
+	preempt_enable();
+	/*
+	 * The barrier() from preempt_enable() prevents the compiler from
+	 * bleeding the critical section out.
+	 */
+}
+
+static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
+{
+	int ret = 1;
+
+	preempt_disable();
+	/*
+	 * Same as in percpu_down_read().
+	 */
+	__this_cpu_inc(*sem->read_count);
+	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
+		ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
+	preempt_enable();
+	/*
+	 * The barrier() from preempt_enable() prevents the compiler from
+	 * bleeding the critical section out.
+	 */
+
+	if (ret)
+		rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
+
+	return ret;
+}
+
+static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
+{
+	/*
+	 * The barrier() in preempt_disable() prevents the compiler from
+	 * bleeding the critical section out.
+	 */
+	preempt_disable();
+	/*
+	 * Same as in percpu_down_read().
+	 */
+	if (likely(rcu_sync_is_idle(&sem->rss)))
+		__this_cpu_dec(*sem->read_count);
+	else
+		__percpu_up_read(sem); /* Unconditional memory barrier */
+	preempt_enable();
+
+	rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
+}
+
+extern void percpu_down_write(struct percpu_rw_semaphore *);
+extern void percpu_up_write(struct percpu_rw_semaphore *);
+
+extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
+				const char *, struct lock_class_key *);
+
+extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
+
+#define percpu_init_rwsem(sem)					\
+({								\
+	static struct lock_class_key rwsem_key;			\
+	__percpu_init_rwsem(sem, #sem, &rwsem_key);		\
+})
+
+#define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
+
+static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
+					bool read, unsigned long ip)
+{
+	lock_release(&sem->rw_sem.dep_map, 1, ip);
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
+	if (!read)
+		sem->rw_sem.owner = NULL;
+#endif
+}
+
+static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
+					bool read, unsigned long ip)
+{
+	lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
+}
+
+#endif