1 files changed, 159 insertions, 0 deletions
diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
new file mode 100644
index 000000000..36b942b67
--- /dev/null
+++ b/include/linux/percpu-rwsem.h
@@ -0,0 +1,159 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PERCPU_RWSEM_H
+#define _LINUX_PERCPU_RWSEM_H
+
+#include <linux/atomic.h>
+#include <linux/percpu.h>
+#include <linux/rcuwait.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 rcuwait		writer;
+	wait_queue_head_t	waiters;
+	atomic_t		block;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map	dep_map;
+#endif
+};
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname)	.dep_map = { .name = #lockname },
+#else
+#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname)
+#endif
+
+#define __DEFINE_PERCPU_RWSEM(name, is_static)				\
+static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);		\
+is_static struct percpu_rw_semaphore name = {				\
+	.rss = __RCU_SYNC_INITIALIZER(name.rss),			\
+	.read_count = &__percpu_rwsem_rc_##name,			\
+	.writer = __RCUWAIT_INITIALIZER(name.writer),			\
+	.waiters = __WAIT_QUEUE_HEAD_INITIALIZER(name.waiters),		\
+	.block = ATOMIC_INIT(0),					\
+	__PERCPU_RWSEM_DEP_MAP_INIT(name)				\
+}
+
+#define DEFINE_PERCPU_RWSEM(name)		\
+	__DEFINE_PERCPU_RWSEM(name, /* not static */)
+#define DEFINE_STATIC_PERCPU_RWSEM(name)	\
+	__DEFINE_PERCPU_RWSEM(name, static)
+
+extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
+
+static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
+{
+	might_sleep();
+
+	rwsem_acquire_read(&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 once the synchronize_rcu() is done, the writer will see
+	 * anything we did within this RCU-sched read-size critical section.
+	 */
+	if (likely(rcu_sync_is_idle(&sem->rss)))
+		this_cpu_inc(*sem->read_count);
+	else
+		__percpu_down_read(sem, false); /* Unconditional memory barrier */
+	/*
+	 * The preempt_enable() prevents the compiler from
+	 * bleeding the critical section out.
+	 */
+	preempt_enable();
+}
+
+static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
+{
+	bool ret = true;
+
+	preempt_disable();
+	/*
+	 * Same as in percpu_down_read().
+	 */
+	if (likely(rcu_sync_is_idle(&sem->rss)))
+		this_cpu_inc(*sem->read_count);
+	else
+		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->dep_map, 0, 1, _RET_IP_);
+
+	return ret;
+}
+
+static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
+{
+	rwsem_release(&sem->dep_map, _RET_IP_);
+
+	preempt_disable();
+	/*
+	 * Same as in percpu_down_read().
+	 */
+	if (likely(rcu_sync_is_idle(&sem->rss))) {
+		this_cpu_dec(*sem->read_count);
+	} else {
+		/*
+		 * slowpath; reader will only ever wake a single blocked
+		 * writer.
+		 */
+		smp_mb(); /* B matches C */
+		/*
+		 * In other words, if they see our decrement (presumably to
+		 * aggregate zero, as that is the only time it matters) they
+		 * will also see our critical section.
+		 */
+		this_cpu_dec(*sem->read_count);
+		rcuwait_wake_up(&sem->writer);
+	}
+	preempt_enable();
+}
+
+extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
+extern void percpu_down_write(struct percpu_rw_semaphore *);
+extern void percpu_up_write(struct percpu_rw_semaphore *);
+
+static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
+{
+	return atomic_read(&sem->block);
+}
+
+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)
+#define percpu_rwsem_assert_held(sem)	lockdep_assert_held(sem)
+
+static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
+					bool read, unsigned long ip)
+{
+	lock_release(&sem->dep_map, ip);
+}
+
+static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
+					bool read, unsigned long ip)
+{
+	lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
+}
+
+#endif