/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * Sleepable Read-Copy Update mechanism for mutual exclusion,
 *      tiny variant.
 *
 * Copyright (C) IBM Corporation, 2017
 *
 * Author: Paul McKenney <paulmck@linux.ibm.com>
 */

#ifndef _LINUX_SRCU_TINY_H
#define _LINUX_SRCU_TINY_H

#include <linux/irq_work_types.h>
#include <linux/swait.h>

struct srcu_struct {
        short srcu_lock_nesting[2];     /* srcu_read_lock() nesting depth. */
        u8 srcu_gp_running;             /* GP workqueue running? */
        u8 srcu_gp_waiting;             /* GP waiting for readers? */
        unsigned long srcu_idx;         /* Current reader array element in bit 0x2. */
        unsigned long srcu_idx_max;     /* Furthest future srcu_idx request. */
        struct swait_queue_head srcu_wq;
                                        /* Last srcu_read_unlock() wakes GP. */
        struct rcu_head *srcu_cb_head;  /* Pending callbacks: Head. */
        struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
        struct work_struct srcu_work;   /* For driving grace periods. */
        struct irq_work srcu_irq_work;  /* Defer schedule_work() to irq work. */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lockdep_map dep_map;
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
};

void srcu_drive_gp(struct work_struct *wp);
void srcu_tiny_irq_work(struct irq_work *irq_work);

#define __SRCU_STRUCT_INIT(name, __ignored, ___ignored, ____ignored)    \
{                                                                       \
        .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),        \
        .srcu_cb_tail = &name.srcu_cb_head,                             \
        .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
        .srcu_irq_work = { .func = srcu_tiny_irq_work },                \
        __SRCU_DEP_MAP_INIT(name)                                       \
}

/*
 * This odd _STATIC_ arrangement is needed for API compatibility with
 * Tree SRCU, which needs some per-CPU data.
 */
#define DEFINE_SRCU(name) \
        struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name)
#define DEFINE_STATIC_SRCU(name) \
        static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name)
#define DEFINE_SRCU_FAST(name) DEFINE_SRCU(name)
#define DEFINE_STATIC_SRCU_FAST(name) \
        static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name)
#define DEFINE_SRCU_FAST_UPDOWN(name) DEFINE_SRCU(name)
#define DEFINE_STATIC_SRCU_FAST_UPDOWN(name) \
        static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name)

// Dummy structure for srcu_notifier_head.
struct srcu_usage { };
#define __SRCU_USAGE_INIT(name) { }
#define __init_srcu_struct_fast __init_srcu_struct
#define __init_srcu_struct_fast_updown __init_srcu_struct
#ifndef CONFIG_DEBUG_LOCK_ALLOC
#define init_srcu_struct_fast init_srcu_struct
#define init_srcu_struct_fast_updown init_srcu_struct
#endif // #ifndef CONFIG_DEBUG_LOCK_ALLOC

void synchronize_srcu(struct srcu_struct *ssp);

/*
 * Counts the new reader in the appropriate per-CPU element of the
 * srcu_struct.  Can be invoked from irq/bh handlers, but the matching
 * __srcu_read_unlock() must be in the same handler instance.  Returns an
 * index that must be passed to the matching srcu_read_unlock().
 */
static inline int __srcu_read_lock(struct srcu_struct *ssp)
        __acquires_shared(ssp)
{
        int idx;

        preempt_disable();  // Needed for PREEMPT_LAZY
        idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
        WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
        preempt_enable();
        __acquire_shared(ssp);
        return idx;
}

struct srcu_ctr;

static inline bool __srcu_ptr_to_ctr(struct srcu_struct *ssp, struct srcu_ctr __percpu *scpp)
{
        return (int)(intptr_t)(struct srcu_ctr __force __kernel *)scpp;
}

static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ssp, int idx)
{
        return (struct srcu_ctr __percpu *)(intptr_t)idx;
}

static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp)
        __acquires_shared(ssp)
{
        return __srcu_ctr_to_ptr(ssp, __srcu_read_lock(ssp));
}

static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
        __releases_shared(ssp)
{
        __srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp));
}

static inline struct srcu_ctr __percpu *__srcu_read_lock_fast_updown(struct srcu_struct *ssp)
        __acquires_shared(ssp)
{
        return __srcu_ctr_to_ptr(ssp, __srcu_read_lock(ssp));
}

static inline
void __srcu_read_unlock_fast_updown(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp)
        __releases_shared(ssp)
{
        __srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp));
}

static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
{
        synchronize_srcu(ssp);
}

static inline void srcu_barrier(struct srcu_struct *ssp)
{
        synchronize_srcu(ssp);
}

static inline void srcu_expedite_current(struct srcu_struct *ssp) { }
#define srcu_check_read_flavor(ssp, read_flavor) do { } while (0)

/* Defined here to avoid size increase for non-torture kernels. */
static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
                                            char *tt, char *tf)
{
        int idx;

        idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
        pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd) gp: %lu->%lu\n",
                 tt, tf, idx,
                 data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
                 data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])),
                 data_race(READ_ONCE(ssp->srcu_idx)),
                 data_race(READ_ONCE(ssp->srcu_idx_max)));
}

#endif