// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Queued read/write locks
 *
 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
 *
 * Authors: Waiman Long <waiman.long@hp.com>
 */
#include <linux/smp.h>
#include <linux/bug.h>
#include <linux/cpumask.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/spinlock.h>
#include <trace/events/lock.h>

/**
 * queued_read_lock_slowpath - acquire read lock of a queued rwlock
 * @lock: Pointer to queued rwlock structure
 */
void __lockfunc queued_read_lock_slowpath(struct qrwlock *lock)
{
        /*
         * Readers come here when they cannot get the lock without waiting
         */
        if (unlikely(in_interrupt())) {
                /*
                 * Readers in interrupt context will get the lock immediately
                 * if the writer is just waiting (not holding the lock yet),
                 * so spin with ACQUIRE semantics until the lock is available
                 * without waiting in the queue.
                 */
                atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
                return;
        }
        atomic_sub(_QR_BIAS, &lock->cnts);

        trace_contention_begin(lock, LCB_F_SPIN | LCB_F_READ);

        /*
         * Put the reader into the wait queue
         */
        arch_spin_lock(&lock->wait_lock);
        atomic_add(_QR_BIAS, &lock->cnts);

        /*
         * The ACQUIRE semantics of the following spinning code ensure
         * that accesses can't leak upwards out of our subsequent critical
         * section in the case that the lock is currently held for write.
         */
        atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));

        /*
         * Signal the next one in queue to become queue head
         */
        arch_spin_unlock(&lock->wait_lock);

        trace_contention_end(lock, 0);
}
EXPORT_SYMBOL(queued_read_lock_slowpath);

/**
 * queued_write_lock_slowpath - acquire write lock of a queued rwlock
 * @lock : Pointer to queued rwlock structure
 */
void __lockfunc queued_write_lock_slowpath(struct qrwlock *lock)
{
        int cnts;

        trace_contention_begin(lock, LCB_F_SPIN | LCB_F_WRITE);

        /* Put the writer into the wait queue */
        arch_spin_lock(&lock->wait_lock);

        /* Try to acquire the lock directly if no reader is present */
        if (!(cnts = atomic_read(&lock->cnts)) &&
            atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))
                goto unlock;

        /* Set the waiting flag to notify readers that a writer is pending */
        atomic_or(_QW_WAITING, &lock->cnts);

        /* When no more readers or writers, set the locked flag */
        do {
                cnts = atomic_cond_read_relaxed(&lock->cnts, VAL == _QW_WAITING);
        } while (!atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED));
unlock:
        arch_spin_unlock(&lock->wait_lock);

        trace_contention_end(lock, 0);
}
EXPORT_SYMBOL(queued_write_lock_slowpath);