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Diffstat (limited to 'arch/ia64/kernel/semaphore.c')
-rw-r--r-- | arch/ia64/kernel/semaphore.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/arch/ia64/kernel/semaphore.c b/arch/ia64/kernel/semaphore.c new file mode 100644 index 00000000000..2724ef3fbae --- /dev/null +++ b/arch/ia64/kernel/semaphore.c @@ -0,0 +1,165 @@ +/* + * IA-64 semaphore implementation (derived from x86 version). + * + * Copyright (C) 1999-2000, 2002 Hewlett-Packard Co + * David Mosberger-Tang <davidm@hpl.hp.com> + */ + +/* + * Semaphores are implemented using a two-way counter: The "count" + * variable is decremented for each process that tries to acquire the + * semaphore, while the "sleepers" variable is a count of such + * acquires. + * + * 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. + * + * "sleeping" and the contention routine ordering is protected + * by the spinlock in the semaphore's waitqueue head. + * + * 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. + */ +#include <linux/sched.h> +#include <linux/init.h> + +#include <asm/errno.h> +#include <asm/semaphore.h> + +/* + * Logic: + * - Only on a boundary condition do we need to care. When we go + * from a negative count to a non-negative, we wake people up. + * - When we go from a non-negative count to a negative do we + * (a) synchronize with the "sleepers" count and (b) make sure + * that we're on the wakeup list before we synchronize so that + * we cannot lose wakeup events. + */ + +void +__up (struct semaphore *sem) +{ + wake_up(&sem->wait); +} + +void __sched __down (struct semaphore *sem) +{ + struct task_struct *tsk = current; + DECLARE_WAITQUEUE(wait, tsk); + unsigned long flags; + + tsk->state = TASK_UNINTERRUPTIBLE; + spin_lock_irqsave(&sem->wait.lock, flags); + add_wait_queue_exclusive_locked(&sem->wait, &wait); + + sem->sleepers++; + for (;;) { + int sleepers = sem->sleepers; + + /* + * Add "everybody else" into it. They aren't + * playing, because we own the spinlock in + * the wait_queue_head. + */ + if (!atomic_add_negative(sleepers - 1, &sem->count)) { + sem->sleepers = 0; + break; + } + sem->sleepers = 1; /* us - see -1 above */ + spin_unlock_irqrestore(&sem->wait.lock, flags); + + schedule(); + + spin_lock_irqsave(&sem->wait.lock, flags); + tsk->state = TASK_UNINTERRUPTIBLE; + } + remove_wait_queue_locked(&sem->wait, &wait); + wake_up_locked(&sem->wait); + spin_unlock_irqrestore(&sem->wait.lock, flags); + tsk->state = TASK_RUNNING; +} + +int __sched __down_interruptible (struct semaphore * sem) +{ + int retval = 0; + struct task_struct *tsk = current; + DECLARE_WAITQUEUE(wait, tsk); + unsigned long flags; + + tsk->state = TASK_INTERRUPTIBLE; + spin_lock_irqsave(&sem->wait.lock, flags); + add_wait_queue_exclusive_locked(&sem->wait, &wait); + + sem->sleepers ++; + for (;;) { + int sleepers = sem->sleepers; + + /* + * With signals pending, this turns into + * the trylock failure case - we won't be + * sleeping, and we* can't get the lock as + * it has contention. Just correct the count + * and exit. + */ + if (signal_pending(current)) { + retval = -EINTR; + sem->sleepers = 0; + atomic_add(sleepers, &sem->count); + break; + } + + /* + * Add "everybody else" into it. They aren't + * playing, because we own the spinlock in + * wait_queue_head. The "-1" is because we're + * still hoping to get the semaphore. + */ + if (!atomic_add_negative(sleepers - 1, &sem->count)) { + sem->sleepers = 0; + break; + } + sem->sleepers = 1; /* us - see -1 above */ + spin_unlock_irqrestore(&sem->wait.lock, flags); + + schedule(); + + spin_lock_irqsave(&sem->wait.lock, flags); + tsk->state = TASK_INTERRUPTIBLE; + } + remove_wait_queue_locked(&sem->wait, &wait); + wake_up_locked(&sem->wait); + spin_unlock_irqrestore(&sem->wait.lock, flags); + + tsk->state = TASK_RUNNING; + return retval; +} + +/* + * Trylock failed - make sure we correct for having decremented the + * count. + */ +int +__down_trylock (struct semaphore *sem) +{ + unsigned long flags; + int sleepers; + + spin_lock_irqsave(&sem->wait.lock, flags); + sleepers = sem->sleepers + 1; + sem->sleepers = 0; + + /* + * Add "everybody else" and us into it. They aren't + * playing, because we own the spinlock in the + * wait_queue_head. + */ + if (!atomic_add_negative(sleepers, &sem->count)) { + wake_up_locked(&sem->wait); + } + + spin_unlock_irqrestore(&sem->wait.lock, flags); + return 1; +} |