arch/s390/kernel/semaphore.c

   1 /*
   2  *  linux/arch/s390/kernel/semaphore.c
   3  *
   4  *  S390 version
   5  *    Copyright (C) 1998-2000 IBM Corporation
   6  *    Author(s): Martin Schwidefsky
   7  *
   8  *  Derived from "linux/arch/i386/kernel/semaphore.c
   9  *    Copyright (C) 1999, Linus Torvalds
  10  *
  11  */
  12 #include <linux/sched.h>
  13 #include <linux/errno.h>
  14 #include <linux/init.h>
  15
  16 #include <asm/semaphore.h>
  17
  18 /*
  19  * Atomically update sem->count. Equivalent to:
  20  *   old_val = sem->count.counter;
  21  *   new_val = ((old_val >= 0) ? old_val : 0) + incr;
  22  *   sem->count.counter = new_val;
  23  *   return old_val;
  24  */
  25 static inline int __sem_update_count(struct semaphore *sem, int incr)
  26 {
  27         int old_val, new_val;
  28
  29         asm volatile(
  30                 "       l       %0,0(%3)\n"
  31                 "0:     ltr     %1,%0\n"
  32                 "       jhe     1f\n"
  33                 "       lhi     %1,0\n"
  34                 "1:     ar      %1,%4\n"
  35                 "       cs      %0,%1,0(%3)\n"
  36                 "       jl      0b\n"
  37                 : "=&d" (old_val), "=&d" (new_val), "=m" (sem->count)
  38                 : "a" (&sem->count), "d" (incr), "m" (sem->count)
  39                 : "cc");
  40         return old_val;
  41 }
  42
  43 /*
  44  * The inline function up() incremented count but the result
  45  * was <= 0. This indicates that some process is waiting on
  46  * the semaphore. The semaphore is free and we'll wake the
  47  * first sleeping process, so we set count to 1 unless some
  48  * other cpu has called up in the meantime in which case
  49  * we just increment count by 1.
  50  */
  51 void __up(struct semaphore *sem)
  52 {
  53         __sem_update_count(sem, 1);
  54         wake_up(&sem->wait);
  55 }
  56
  57 /*
  58  * The inline function down() decremented count and the result
  59  * was < 0. The wait loop will atomically test and update the
  60  * semaphore counter following the rules:
  61  *   count > 0: decrement count, wake up queue and exit.
  62  *   count <= 0: set count to -1, go to sleep.
  63  */
  64 void __sched __down(struct semaphore * sem)
  65 {
  66         struct task_struct *tsk = current;
  67         DECLARE_WAITQUEUE(wait, tsk);
  68
  69         __set_task_state(tsk, TASK_UNINTERRUPTIBLE);
  70         add_wait_queue_exclusive(&sem->wait, &wait);
  71         while (__sem_update_count(sem, -1) <= 0) {
  72                 schedule();
  73                 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
  74         }
  75         remove_wait_queue(&sem->wait, &wait);
  76         __set_task_state(tsk, TASK_RUNNING);
  77         wake_up(&sem->wait);
  78 }
  79
  80 /*
  81  * Same as __down() with an additional test for signals.
  82  * If a signal is pending the count is updated as follows:
  83  *   count > 0: wake up queue and exit.
  84  *   count <= 0: set count to 0, wake up queue and exit.
  85  */
  86 int __sched __down_interruptible(struct semaphore * sem)
  87 {
  88         int retval = 0;
  89         struct task_struct *tsk = current;
  90         DECLARE_WAITQUEUE(wait, tsk);
  91
  92         __set_task_state(tsk, TASK_INTERRUPTIBLE);
  93         add_wait_queue_exclusive(&sem->wait, &wait);
  94         while (__sem_update_count(sem, -1) <= 0) {
  95                 if (signal_pending(current)) {
  96                         __sem_update_count(sem, 0);
  97                         retval = -EINTR;
  98                         break;
  99                 }
 100                 schedule();
 101                 set_task_state(tsk, TASK_INTERRUPTIBLE);
 102         }
 103         remove_wait_queue(&sem->wait, &wait);
 104         __set_task_state(tsk, TASK_RUNNING);
 105         wake_up(&sem->wait);
 106         return retval;
 107 }
 108