arch/nios2nommu/kernel/semaphore.c

   1 /*--------------------------------------------------------------------
   2  *
   3  * arch/nios2nommu/kernel/semaphore.c
   4  *
   5  * Derived from various works, Alpha, ix86, M68K, Sparc, ...et al
   6  *
   7  * Copyright (C) 2004   Microtronix Datacom Ltd
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License as published by
  11  * the Free Software Foundation; either version 2 of the License, or
  12  * (at your option) any later version.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  *
  20  * Jan/20/2004          dgt         NiosII
  21  *
  22  ---------------------------------------------------------------------*/
  23
  24 /*
  25  *  Generic semaphore code. Buyer beware. Do your own
  26  * specific changes in <asm/semaphore-helper.h>
  27  */
  28
  29 #include <linux/sched.h>
  30 #include <linux/err.h>
  31 #include <asm/semaphore-helper.h>
  32
  33 #ifndef CONFIG_RMW_INSNS
  34 spinlock_t semaphore_wake_lock;
  35 #endif
  36
  37 /*
  38  * Semaphores are implemented using a two-way counter:
  39  * The "count" variable is decremented for each process
  40  * that tries to sleep, while the "waking" variable is
  41  * incremented when the "up()" code goes to wake up waiting
  42  * processes.
  43  *
  44  * Notably, the inline "up()" and "down()" functions can
  45  * efficiently test if they need to do any extra work (up
  46  * needs to do something only if count was negative before
  47  * the increment operation.
  48  *
  49  * waking_non_zero() (from asm/semaphore.h) must execute
  50  * atomically.
  51  *
  52  * When __up() is called, the count was negative before
  53  * incrementing it, and we need to wake up somebody.
  54  *
  55  * This routine adds one to the count of processes that need to
  56  * wake up and exit.  ALL waiting processes actually wake up but
  57  * only the one that gets to the "waking" field first will gate
  58  * through and acquire the semaphore.  The others will go back
  59  * to sleep.
  60  *
  61  * Note that these functions are only called when there is
  62  * contention on the lock, and as such all this is the
  63  * "non-critical" part of the whole semaphore business. The
  64  * critical part is the inline stuff in <asm/semaphore.h>
  65  * where we want to avoid any extra jumps and calls.
  66  */
  67 asmlinkage void __up(struct semaphore *sem)
  68 {
  69         wake_one_more(sem);
  70         wake_up(&sem->wait);
  71 }
  72
  73 /*
  74  * Perform the "down" function.  Return zero for semaphore acquired,
  75  * return negative for signalled out of the function.
  76  *
  77  * If called from __down, the return is ignored and the wait loop is
  78  * not interruptible.  This means that a task waiting on a semaphore
  79  * using "down()" cannot be killed until someone does an "up()" on
  80  * the semaphore.
  81  *
  82  * If called from __down_interruptible, the return value gets checked
  83  * upon return.  If the return value is negative then the task continues
  84  * with the negative value in the return register (it can be tested by
  85  * the caller).
  86  *
  87  * Either form may be used in conjunction with "up()".
  88  *
  89  */
  90
  91
  92 #define DOWN_HEAD(task_state)                                           \
  93                                                                         \
  94                                                                         \
  95         current->state = (task_state);                                  \
  96         add_wait_queue(&sem->wait, &wait);                              \
  97                                                                         \
  98         /*                                                              \
  99          * Ok, we're set up.  sem->count is known to be less than zero  \
 100          * so we must wait.                                             \
 101          *                                                              \
 102          * We can let go the lock for purposes of waiting.              \
 103          * We re-acquire it after awaking so as to protect              \
 104          * all semaphore operations.                                    \
 105          *                                                              \
 106          * If "up()" is called before we call waking_non_zero() then    \
 107          * we will catch it right away.  If it is called later then     \
 108          * we will have to go through a wakeup cycle to catch it.       \
 109          *                                                              \
 110          * Multiple waiters contend for the semaphore lock to see       \
 111          * who gets to gate through and who has to wait some more.      \
 112          */                                                             \
 113         for (;;) {
 114
 115 #define DOWN_TAIL(task_state)                   \
 116                 current->state = (task_state);  \
 117         }                                       \
 118         current->state = TASK_RUNNING;          \
 119         remove_wait_queue(&sem->wait, &wait);
 120
 121 void __sched __down(struct semaphore * sem)
 122 {
 123         DECLARE_WAITQUEUE(wait, current);
 124
 125         DOWN_HEAD(TASK_UNINTERRUPTIBLE)
 126         if (waking_non_zero(sem))
 127                 break;
 128         schedule();
 129         DOWN_TAIL(TASK_UNINTERRUPTIBLE)
 130 }
 131
 132 int __sched __down_interruptible(struct semaphore * sem)
 133 {
 134         DECLARE_WAITQUEUE(wait, current);
 135         int ret = 0;
 136
 137         DOWN_HEAD(TASK_INTERRUPTIBLE)
 138
 139         ret = waking_non_zero_interruptible(sem, current);
 140         if (ret)
 141         {
 142                 if (ret == 1)
 143                         /* ret != 0 only if we get interrupted -arca */
 144                         ret = 0;
 145                 break;
 146         }
 147         schedule();
 148         DOWN_TAIL(TASK_INTERRUPTIBLE)
 149         return ret;
 150 }
 151
 152 int __down_trylock(struct semaphore * sem)
 153 {
 154         return waking_non_zero_trylock(sem);
 155 }