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  */
  30 extern void queued_read_lock_slowpath(struct qrwlock *lock);
  31 extern 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  */
  38 static inline int queued_read_trylock(struct qrwlock *lock)
  39 {
  40         int 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  */
  57 static inline int queued_write_trylock(struct qrwlock *lock)
  58 {
  59         int 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  */
  72 static inline void queued_read_lock(struct qrwlock *lock)
  73 {
  74         int 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  */
  88 static inline void queued_write_lock(struct qrwlock *lock)
  89 {
  90         int 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  */
 102 static 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  */
 114 static 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 */