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