/* 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>
#include <linux/cleanup.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, bool);

static inline void percpu_down_read_internal(struct percpu_rw_semaphore *sem,
                                             bool freezable)
{
        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, freezable); /* Unconditional memory barrier */
        /*
         * The preempt_enable() prevents the compiler from
         * bleeding the critical section out.
         */
        preempt_enable();
}

static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
{
        percpu_down_read_internal(sem, false);
}

static inline void percpu_down_read_freezable(struct percpu_rw_semaphore *sem,
                                              bool freeze)
{
        percpu_down_read_internal(sem, freeze);
}

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, false); /* 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 *);

DEFINE_GUARD(percpu_read, struct percpu_rw_semaphore *,
             percpu_down_read(_T), percpu_up_read(_T))
DEFINE_GUARD_COND(percpu_read, _try, percpu_down_read_trylock(_T))

DEFINE_GUARD(percpu_write, struct percpu_rw_semaphore *,
             percpu_down_write(_T), percpu_up_write(_T))

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_write_held(sem) lockdep_is_held_type(sem, 0)
#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,
                                        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