// 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);