arch/sh64/kernel/semaphore.c

   1 /*
   2  * Just taken from alpha implementation.
   3  * This can't work well, perhaps.
   4  */
   5 /*
   6  *  Generic semaphore code. Buyer beware. Do your own
   7  * specific changes in <asm/semaphore-helper.h>
   8  */
   9
  10 #include <linux/errno.h>
  11 #include <linux/rwsem.h>
  12 #include <linux/sched.h>
  13 #include <linux/wait.h>
  14 #include <linux/init.h>
  15 #include <asm/semaphore.h>
  16 #include <asm/semaphore-helper.h>
  17
  18 spinlock_t semaphore_wake_lock;
  19
  20 /*
  21  * Semaphores are implemented using a two-way counter:
  22  * The "count" variable is decremented for each process
  23  * that tries to sleep, while the "waking" variable is
  24  * incremented when the "up()" code goes to wake up waiting
  25  * processes.
  26  *
  27  * Notably, the inline "up()" and "down()" functions can
  28  * efficiently test if they need to do any extra work (up
  29  * needs to do something only if count was negative before
  30  * the increment operation.
  31  *
  32  * waking_non_zero() (from asm/semaphore.h) must execute
  33  * atomically.
  34  *
  35  * When __up() is called, the count was negative before
  36  * incrementing it, and we need to wake up somebody.
  37  *
  38  * This routine adds one to the count of processes that need to
  39  * wake up and exit.  ALL waiting processes actually wake up but
  40  * only the one that gets to the "waking" field first will gate
  41  * through and acquire the semaphore.  The others will go back
  42  * to sleep.
  43  *
  44  * Note that these functions are only called when there is
  45  * contention on the lock, and as such all this is the
  46  * "non-critical" part of the whole semaphore business. The
  47  * critical part is the inline stuff in <asm/semaphore.h>
  48  * where we want to avoid any extra jumps and calls.
  49  */
  50 void __up(struct semaphore *sem)
  51 {
  52         wake_one_more(sem);
  53         wake_up(&sem->wait);
  54 }
  55
  56 /*
  57  * Perform the "down" function.  Return zero for semaphore acquired,
  58  * return negative for signalled out of the function.
  59  *
  60  * If called from __down, the return is ignored and the wait loop is
  61  * not interruptible.  This means that a task waiting on a semaphore
  62  * using "down()" cannot be killed until someone does an "up()" on
  63  * the semaphore.
  64  *
  65  * If called from __down_interruptible, the return value gets checked
  66  * upon return.  If the return value is negative then the task continues
  67  * with the negative value in the return register (it can be tested by
  68  * the caller).
  69  *
  70  * Either form may be used in conjunction with "up()".
  71  *
  72  */
  73
  74 #define DOWN_VAR                                \
  75         struct task_struct *tsk = current;      \
  76         wait_queue_t wait;                      \
  77         init_waitqueue_entry(&wait, tsk);
  78
  79 #define DOWN_HEAD(task_state)                                           \
  80                                                                         \
  81                                                                         \
  82         tsk->state = (task_state);                                      \
  83         add_wait_queue(&sem->wait, &wait);                              \
  84                                                                         \
  85         /*                                                              \
  86          * Ok, we're set up.  sem->count is known to be less than zero  \
  87          * so we must wait.                                             \
  88          *                                                              \
  89          * We can let go the lock for purposes of waiting.              \
  90          * We re-acquire it after awaking so as to protect              \
  91          * all semaphore operations.                                    \
  92          *                                                              \
  93          * If "up()" is called before we call waking_non_zero() then    \
  94          * we will catch it right away.  If it is called later then     \
  95          * we will have to go through a wakeup cycle to catch it.       \
  96          *                                                              \
  97          * Multiple waiters contend for the semaphore lock to see       \
  98          * who gets to gate through and who has to wait some more.      \
  99          */                                                             \
 100         for (;;) {
 101
 102 #define DOWN_TAIL(task_state)                   \
 103                 tsk->state = (task_state);      \
 104         }                                       \
 105         tsk->state = TASK_RUNNING;              \
 106         remove_wait_queue(&sem->wait, &wait);
 107
 108 void __sched __down(struct semaphore * sem)
 109 {
 110         DOWN_VAR
 111         DOWN_HEAD(TASK_UNINTERRUPTIBLE)
 112         if (waking_non_zero(sem))
 113                 break;
 114         schedule();
 115         DOWN_TAIL(TASK_UNINTERRUPTIBLE)
 116 }
 117
 118 int __sched __down_interruptible(struct semaphore * sem)
 119 {
 120         int ret = 0;
 121         DOWN_VAR
 122         DOWN_HEAD(TASK_INTERRUPTIBLE)
 123
 124         ret = waking_non_zero_interruptible(sem, tsk);
 125         if (ret)
 126         {
 127                 if (ret == 1)
 128                         /* ret != 0 only if we get interrupted -arca */
 129                         ret = 0;
 130                 break;
 131         }
 132         schedule();
 133         DOWN_TAIL(TASK_INTERRUPTIBLE)
 134         return ret;
 135 }
 136
 137 int __down_trylock(struct semaphore * sem)
 138 {
 139         return waking_non_zero_trylock(sem);
 140 }