// SPDX-License-Identifier: GPL-2.0+
/*
 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
 *
 * Copyright IBM Corporation, 2008
 *
 * Author: Paul E. McKenney <paulmck@linux.ibm.com>
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 *              Documentation/RCU
 */
#include <linux/completion.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/rcupdate_wait.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/time.h>
#include <linux/cpu.h>
#include <linux/prefetch.h>
#include <linux/slab.h>
#include <linux/mm.h>

#include "rcu.h"

/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
        struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
        struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
        struct rcu_head **curtail;      /* ->next pointer of last CB. */
        unsigned long gp_seq;           /* Grace-period counter. */
};

/* Definition for rcupdate control block. */
static struct rcu_ctrlblk rcu_ctrlblk = {
        .donetail       = &rcu_ctrlblk.rcucblist,
        .curtail        = &rcu_ctrlblk.rcucblist,
        .gp_seq         = 0 - 300UL,
};

void rcu_barrier(void)
{
        wait_rcu_gp(call_rcu_hurry);
}
EXPORT_SYMBOL(rcu_barrier);

/* Record an rcu quiescent state.  */
void rcu_qs(void)
{
        unsigned long flags;

        local_irq_save(flags);
        if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
                rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
                raise_softirq_irqoff(RCU_SOFTIRQ);
        }
        WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);
        local_irq_restore(flags);
}

/*
 * Check to see if the scheduling-clock interrupt came from an extended
 * quiescent state, and, if so, tell RCU about it.  This function must
 * be called from hardirq context.  It is normally called from the
 * scheduling-clock interrupt.
 */
void rcu_sched_clock_irq(int user)
{
        if (user)
                rcu_qs();
        else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail)
                set_need_resched_current();
}

/*
 * Reclaim the specified callback, either by invoking it for non-kfree cases or
 * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
 */
static inline bool rcu_reclaim_tiny(struct rcu_head *head)
{
        rcu_callback_t f;

        rcu_lock_acquire(&rcu_callback_map);

        trace_rcu_invoke_callback("", head);
        f = head->func;
        debug_rcu_head_callback(head);
        WRITE_ONCE(head->func, (rcu_callback_t)0L);
        f(head);
        rcu_lock_release(&rcu_callback_map);
        return false;
}

/* Invoke the RCU callbacks whose grace period has elapsed.  */
static __latent_entropy void rcu_process_callbacks(void)
{
        struct rcu_head *next, *list;
        unsigned long flags;

        /* Move the ready-to-invoke callbacks to a local list. */
        local_irq_save(flags);
        if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
                /* No callbacks ready, so just leave. */
                local_irq_restore(flags);
                return;
        }
        list = rcu_ctrlblk.rcucblist;
        rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
        *rcu_ctrlblk.donetail = NULL;
        if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
                rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
        rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
        local_irq_restore(flags);

        /* Invoke the callbacks on the local list. */
        while (list) {
                next = list->next;
                prefetch(next);
                debug_rcu_head_unqueue(list);
                rcu_reclaim_tiny(list);
                list = next;
        }
}

/*
 * Wait for a grace period to elapse.  But it is illegal to invoke
 * synchronize_rcu() from within an RCU read-side critical section.
 * Therefore, any legal call to synchronize_rcu() is a quiescent state,
 * and so on a UP system, synchronize_rcu() need do nothing, other than
 * let the polled APIs know that another grace period elapsed.
 *
 * (But Lai Jiangshan points out the benefits of doing might_sleep()
 * to reduce latency.)
 *
 * Cool, huh?  (Due to Josh Triplett.)
 */
void synchronize_rcu(void)
{
        RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
                         lock_is_held(&rcu_lock_map) ||
                         lock_is_held(&rcu_sched_lock_map),
                         "Illegal synchronize_rcu() in RCU read-side critical section");
        preempt_disable();
        WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);
        preempt_enable();
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

/*
 * Post an RCU callback to be invoked after the end of an RCU grace
 * period.  But since we have but one CPU, that would be after any
 * quiescent state.
 */
void call_rcu(struct rcu_head *head, rcu_callback_t func)
{
        static atomic_t doublefrees;
        unsigned long flags;

        if (debug_rcu_head_queue(head)) {
                if (atomic_inc_return(&doublefrees) < 4) {
                        pr_err("%s(): Double-freed CB %p->%pS()!!!  ", __func__, head, head->func);
                        mem_dump_obj(head);
                }
                return;
        }

        head->func = func;
        head->next = NULL;

        local_irq_save(flags);
        *rcu_ctrlblk.curtail = head;
        rcu_ctrlblk.curtail = &head->next;
        local_irq_restore(flags);

        if (unlikely(is_idle_task(current))) {
                /* force scheduling for rcu_qs() */
                resched_cpu(0);
        }
}
EXPORT_SYMBOL_GPL(call_rcu);

/*
 * Store a grace-period-counter "cookie".  For more information,
 * see the Tree RCU header comment.
 */
void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
{
        rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
}
EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);

/*
 * Return a grace-period-counter "cookie".  For more information,
 * see the Tree RCU header comment.
 */
unsigned long get_state_synchronize_rcu(void)
{
        return READ_ONCE(rcu_ctrlblk.gp_seq);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);

/*
 * Return a grace-period-counter "cookie" and ensure that a future grace
 * period completes.  For more information, see the Tree RCU header comment.
 */
unsigned long start_poll_synchronize_rcu(void)
{
        unsigned long gp_seq = get_state_synchronize_rcu();

        if (unlikely(is_idle_task(current))) {
                /* force scheduling for rcu_qs() */
                resched_cpu(0);
        }
        return gp_seq;
}
EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);

/*
 * Return true if the grace period corresponding to oldstate has completed
 * and false otherwise.  For more information, see the Tree RCU header
 * comment.
 */
bool poll_state_synchronize_rcu(unsigned long oldstate)
{
        return oldstate == RCU_GET_STATE_COMPLETED || READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate;
}
EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);

#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST)
unsigned long long rcutorture_gather_gp_seqs(void)
{
        return READ_ONCE(rcu_ctrlblk.gp_seq) & 0xffffULL;
}
EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);

void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len)
{
        snprintf(cp, len, "g%04llx", seqs & 0xffffULL);
}
EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);
#endif

void __init rcu_init(void)
{
        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
        rcu_early_boot_tests();
        tasks_cblist_init_generic();
}