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/arch/sh/kernel/semaphore.c

https://bitbucket.org/evzijst/gittest
C | 139 lines | 58 code | 11 blank | 70 comment | 5 complexity | 22f1827b346e83fefc9472b387c9c4c1 MD5 | raw file
  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/sched.h>
 12#include <linux/wait.h>
 13#include <linux/init.h>
 14#include <asm/semaphore.h>
 15#include <asm/semaphore-helper.h>
 16
 17spinlock_t semaphore_wake_lock;
 18
 19/*
 20 * Semaphores are implemented using a two-way counter:
 21 * The "count" variable is decremented for each process
 22 * that tries to sleep, while the "waking" variable is
 23 * incremented when the "up()" code goes to wake up waiting
 24 * processes.
 25 *
 26 * Notably, the inline "up()" and "down()" functions can
 27 * efficiently test if they need to do any extra work (up
 28 * needs to do something only if count was negative before
 29 * the increment operation.
 30 *
 31 * waking_non_zero() (from asm/semaphore.h) must execute
 32 * atomically.
 33 *
 34 * When __up() is called, the count was negative before
 35 * incrementing it, and we need to wake up somebody.
 36 *
 37 * This routine adds one to the count of processes that need to
 38 * wake up and exit.  ALL waiting processes actually wake up but
 39 * only the one that gets to the "waking" field first will gate
 40 * through and acquire the semaphore.  The others will go back
 41 * to sleep.
 42 *
 43 * Note that these functions are only called when there is
 44 * contention on the lock, and as such all this is the
 45 * "non-critical" part of the whole semaphore business. The
 46 * critical part is the inline stuff in <asm/semaphore.h>
 47 * where we want to avoid any extra jumps and calls.
 48 */
 49void __up(struct semaphore *sem)
 50{
 51	wake_one_more(sem);
 52	wake_up(&sem->wait);
 53}
 54
 55/*
 56 * Perform the "down" function.  Return zero for semaphore acquired,
 57 * return negative for signalled out of the function.
 58 *
 59 * If called from __down, the return is ignored and the wait loop is
 60 * not interruptible.  This means that a task waiting on a semaphore
 61 * using "down()" cannot be killed until someone does an "up()" on
 62 * the semaphore.
 63 *
 64 * If called from __down_interruptible, the return value gets checked
 65 * upon return.  If the return value is negative then the task continues
 66 * with the negative value in the return register (it can be tested by
 67 * the caller).
 68 *
 69 * Either form may be used in conjunction with "up()".
 70 *
 71 */
 72
 73#define DOWN_VAR				\
 74	struct task_struct *tsk = current;	\
 75	wait_queue_t wait;			\
 76	init_waitqueue_entry(&wait, tsk);
 77
 78#define DOWN_HEAD(task_state)						\
 79									\
 80									\
 81	tsk->state = (task_state);					\
 82	add_wait_queue(&sem->wait, &wait);				\
 83									\
 84	/*								\
 85	 * Ok, we're set up.  sem->count is known to be less than zero	\
 86	 * so we must wait.						\
 87	 *								\
 88	 * We can let go the lock for purposes of waiting.		\
 89	 * We re-acquire it after awaking so as to protect		\
 90	 * all semaphore operations.					\
 91	 *								\
 92	 * If "up()" is called before we call waking_non_zero() then	\
 93	 * we will catch it right away.  If it is called later then	\
 94	 * we will have to go through a wakeup cycle to catch it.	\
 95	 *								\
 96	 * Multiple waiters contend for the semaphore lock to see	\
 97	 * who gets to gate through and who has to wait some more.	\
 98	 */								\
 99	for (;;) {
100
101#define DOWN_TAIL(task_state)			\
102		tsk->state = (task_state);	\
103	}					\
104	tsk->state = TASK_RUNNING;		\
105	remove_wait_queue(&sem->wait, &wait);
106
107void __sched __down(struct semaphore * sem)
108{
109	DOWN_VAR
110	DOWN_HEAD(TASK_UNINTERRUPTIBLE)
111	if (waking_non_zero(sem))
112		break;
113	schedule();
114	DOWN_TAIL(TASK_UNINTERRUPTIBLE)
115}
116
117int __sched __down_interruptible(struct semaphore * sem)
118{
119	int ret = 0;
120	DOWN_VAR
121	DOWN_HEAD(TASK_INTERRUPTIBLE)
122
123	ret = waking_non_zero_interruptible(sem, tsk);
124	if (ret)
125	{
126		if (ret == 1)
127			/* ret != 0 only if we get interrupted -arca */
128			ret = 0;
129		break;
130	}
131	schedule();
132	DOWN_TAIL(TASK_INTERRUPTIBLE)
133	return ret;
134}
135
136int __down_trylock(struct semaphore * sem)
137{
138	return waking_non_zero_trylock(sem);
139}