diff options
Diffstat (limited to 'arch/sh/kernel/semaphore.c')
-rw-r--r-- | arch/sh/kernel/semaphore.c | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/arch/sh/kernel/semaphore.c b/arch/sh/kernel/semaphore.c new file mode 100644 index 0000000..a3c24dc --- /dev/null +++ b/arch/sh/kernel/semaphore.c @@ -0,0 +1,139 @@ +/* + * 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); +} |