LXR linux/include/asm-generic/qrwlock.h

   1/* SPDX-License-Identifier: GPL-2.0-or-later */
   2/*
   3 * Queue read/write lock
   4 *
   5 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
   6 *
   7 * Authors: Waiman Long <waiman.long@hp.com>
   8 */
   9#ifndef __ASM_GENERIC_QRWLOCK_H
  10#define __ASM_GENERIC_QRWLOCK_H
  11
  12#include <linux/atomic.h>
  13#include <asm/barrier.h>
  14#include <asm/processor.h>
  15
  16#include <asm-generic/qrwlock_types.h>
  17
  18/*
  19 * Writer states & reader shift and bias.
  20 */
  21#define _QW_WAITING     0x100           /* A writer is waiting     */
  22#define _QW_LOCKED      0x0ff           /* A writer holds the lock */
  23#define _QW_WMASK       0x1ff           /* Writer mask             */
  24#define _QR_SHIFT       9               /* Reader count shift      */
  25#define _QR_BIAS        (1U << _QR_SHIFT)
  26
  27/*
  28 * External function declarations
  29 */
  30extern void queued_read_lock_slowpath(struct qrwlock *lock);
  31extern void queued_write_lock_slowpath(struct qrwlock *lock);
  32
  33/**
  34 * queued_read_trylock - try to acquire read lock of a queue rwlock
  35 * @lock : Pointer to queue rwlock structure
  36 * Return: 1 if lock acquired, 0 if failed
  37 */
  38static inline int queued_read_trylock(struct qrwlock *lock)
  39{
  40        u32 cnts;
  41
  42        cnts = atomic_read(&lock->cnts);
  43        if (likely(!(cnts & _QW_WMASK))) {
  44                cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
  45                if (likely(!(cnts & _QW_WMASK)))
  46                        return 1;
  47                atomic_sub(_QR_BIAS, &lock->cnts);
  48        }
  49        return 0;
  50}
  51
  52/**
  53 * queued_write_trylock - try to acquire write lock of a queue rwlock
  54 * @lock : Pointer to queue rwlock structure
  55 * Return: 1 if lock acquired, 0 if failed
  56 */
  57static inline int queued_write_trylock(struct qrwlock *lock)
  58{
  59        u32 cnts;
  60
  61        cnts = atomic_read(&lock->cnts);
  62        if (unlikely(cnts))
  63                return 0;
  64
  65        return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
  66                                _QW_LOCKED));
  67}
  68/**
  69 * queued_read_lock - acquire read lock of a queue rwlock
  70 * @lock: Pointer to queue rwlock structure
  71 */
  72static inline void queued_read_lock(struct qrwlock *lock)
  73{
  74        u32 cnts;
  75
  76        cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
  77        if (likely(!(cnts & _QW_WMASK)))
  78                return;
  79
  80        /* The slowpath will decrement the reader count, if necessary. */
  81        queued_read_lock_slowpath(lock);
  82}
  83
  84/**
  85 * queued_write_lock - acquire write lock of a queue rwlock
  86 * @lock : Pointer to queue rwlock structure
  87 */
  88static inline void queued_write_lock(struct qrwlock *lock)
  89{
  90        u32 cnts = 0;
  91        /* Optimize for the unfair lock case where the fair flag is 0. */
  92        if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
  93                return;
  94
  95        queued_write_lock_slowpath(lock);
  96}
  97
  98/**
  99 * queued_read_unlock - release read lock of a queue rwlock
 100 * @lock : Pointer to queue rwlock structure
 101 */
 102static inline void queued_read_unlock(struct qrwlock *lock)
 103{
 104        /*
 105         * Atomically decrement the reader count
 106         */
 107        (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
 108}
 109
 110/**
 111 * queued_write_unlock - release write lock of a queue rwlock
 112 * @lock : Pointer to queue rwlock structure
 113 */
 114static inline void queued_write_unlock(struct qrwlock *lock)
 115{
 116        smp_store_release(&lock->wlocked, 0);
 117}
 118
 119/*
 120 * Remapping rwlock architecture specific functions to the corresponding
 121 * queue rwlock functions.
 122 */
 123#define arch_read_lock(l)       queued_read_lock(l)
 124#define arch_write_lock(l)      queued_write_lock(l)
 125#define arch_read_trylock(l)    queued_read_trylock(l)
 126#define arch_write_trylock(l)   queued_write_trylock(l)
 127#define arch_read_unlock(l)     queued_read_unlock(l)
 128#define arch_write_unlock(l)    queued_write_unlock(l)
 129
 130#endif /* __ASM_GENERIC_QRWLOCK_H */
 131