140 строки
3.8 KiB
C
140 строки
3.8 KiB
C
/*
|
|
* Just taken from alpha implementation.
|
|
* This can't work well, perhaps.
|
|
*/
|
|
/*
|
|
* Generic semaphore code. Buyer beware. Do your own
|
|
* specific changes in <asm/semaphore-helper.h>
|
|
*/
|
|
|
|
#include <linux/errno.h>
|
|
#include <linux/sched.h>
|
|
#include <linux/wait.h>
|
|
#include <linux/init.h>
|
|
#include <asm/semaphore.h>
|
|
#include <asm/semaphore-helper.h>
|
|
|
|
spinlock_t semaphore_wake_lock;
|
|
|
|
/*
|
|
* Semaphores are implemented using a two-way counter:
|
|
* The "count" variable is decremented for each process
|
|
* that tries to sleep, while the "waking" variable is
|
|
* incremented when the "up()" code goes to wake up waiting
|
|
* processes.
|
|
*
|
|
* Notably, the inline "up()" and "down()" functions can
|
|
* efficiently test if they need to do any extra work (up
|
|
* needs to do something only if count was negative before
|
|
* the increment operation.
|
|
*
|
|
* waking_non_zero() (from asm/semaphore.h) must execute
|
|
* atomically.
|
|
*
|
|
* When __up() is called, the count was negative before
|
|
* incrementing it, and we need to wake up somebody.
|
|
*
|
|
* This routine adds one to the count of processes that need to
|
|
* wake up and exit. ALL waiting processes actually wake up but
|
|
* only the one that gets to the "waking" field first will gate
|
|
* through and acquire the semaphore. The others will go back
|
|
* to sleep.
|
|
*
|
|
* Note that these functions are only called when there is
|
|
* contention on the lock, and as such all this is the
|
|
* "non-critical" part of the whole semaphore business. The
|
|
* critical part is the inline stuff in <asm/semaphore.h>
|
|
* where we want to avoid any extra jumps and calls.
|
|
*/
|
|
void __up(struct semaphore *sem)
|
|
{
|
|
wake_one_more(sem);
|
|
wake_up(&sem->wait);
|
|
}
|
|
|
|
/*
|
|
* Perform the "down" function. Return zero for semaphore acquired,
|
|
* return negative for signalled out of the function.
|
|
*
|
|
* If called from __down, the return is ignored and the wait loop is
|
|
* not interruptible. This means that a task waiting on a semaphore
|
|
* using "down()" cannot be killed until someone does an "up()" on
|
|
* the semaphore.
|
|
*
|
|
* If called from __down_interruptible, the return value gets checked
|
|
* upon return. If the return value is negative then the task continues
|
|
* with the negative value in the return register (it can be tested by
|
|
* the caller).
|
|
*
|
|
* Either form may be used in conjunction with "up()".
|
|
*
|
|
*/
|
|
|
|
#define DOWN_VAR \
|
|
struct task_struct *tsk = current; \
|
|
wait_queue_t wait; \
|
|
init_waitqueue_entry(&wait, tsk);
|
|
|
|
#define DOWN_HEAD(task_state) \
|
|
\
|
|
\
|
|
tsk->state = (task_state); \
|
|
add_wait_queue(&sem->wait, &wait); \
|
|
\
|
|
/* \
|
|
* Ok, we're set up. sem->count is known to be less than zero \
|
|
* so we must wait. \
|
|
* \
|
|
* We can let go the lock for purposes of waiting. \
|
|
* We re-acquire it after awaking so as to protect \
|
|
* all semaphore operations. \
|
|
* \
|
|
* If "up()" is called before we call waking_non_zero() then \
|
|
* we will catch it right away. If it is called later then \
|
|
* we will have to go through a wakeup cycle to catch it. \
|
|
* \
|
|
* Multiple waiters contend for the semaphore lock to see \
|
|
* who gets to gate through and who has to wait some more. \
|
|
*/ \
|
|
for (;;) {
|
|
|
|
#define DOWN_TAIL(task_state) \
|
|
tsk->state = (task_state); \
|
|
} \
|
|
tsk->state = TASK_RUNNING; \
|
|
remove_wait_queue(&sem->wait, &wait);
|
|
|
|
void __sched __down(struct semaphore * sem)
|
|
{
|
|
DOWN_VAR
|
|
DOWN_HEAD(TASK_UNINTERRUPTIBLE)
|
|
if (waking_non_zero(sem))
|
|
break;
|
|
schedule();
|
|
DOWN_TAIL(TASK_UNINTERRUPTIBLE)
|
|
}
|
|
|
|
int __sched __down_interruptible(struct semaphore * sem)
|
|
{
|
|
int ret = 0;
|
|
DOWN_VAR
|
|
DOWN_HEAD(TASK_INTERRUPTIBLE)
|
|
|
|
ret = waking_non_zero_interruptible(sem, tsk);
|
|
if (ret)
|
|
{
|
|
if (ret == 1)
|
|
/* ret != 0 only if we get interrupted -arca */
|
|
ret = 0;
|
|
break;
|
|
}
|
|
schedule();
|
|
DOWN_TAIL(TASK_INTERRUPTIBLE)
|
|
return ret;
|
|
}
|
|
|
|
int __down_trylock(struct semaphore * sem)
|
|
{
|
|
return waking_non_zero_trylock(sem);
|
|
}
|