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 18spinlock_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 */ 50void __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 108void __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 118int __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 137int __down_trylock(struct semaphore * sem) 138{ 139 return waking_non_zero_trylock(sem); 140} 141