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Diffstat (limited to 'arch/v850/kernel/semaphore.c')
| -rw-r--r-- | arch/v850/kernel/semaphore.c | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/arch/v850/kernel/semaphore.c b/arch/v850/kernel/semaphore.c new file mode 100644 index 00000000000..fc89fd661c9 --- /dev/null +++ b/arch/v850/kernel/semaphore.c @@ -0,0 +1,166 @@ +/* + * arch/v850/kernel/semaphore.c -- Semaphore support + * + * Copyright (C) 1998-2000 IBM Corporation + * Copyright (C) 1999 Linus Torvalds + * + * This file is subject to the terms and conditions of the GNU General + * Public License. See the file COPYING in the main directory of this + * archive for more details. + * + * This file is a copy of the s390 version, arch/s390/kernel/semaphore.c + * Author(s): Martin Schwidefsky + * which was derived from the i386 version, linux/arch/i386/kernel/semaphore.c + */ + +#include <linux/errno.h> +#include <linux/sched.h> +#include <linux/init.h> + +#include <asm/semaphore.h> + +/* + * Semaphores are implemented using a two-way counter: + * The "count" variable is decremented for each process + * that tries to acquire the semaphore, while the "sleeping" + * 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 semaphore spinlock. + * + * 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. + */ + +/* + * 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 "sleeper" 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); +} + +static DEFINE_SPINLOCK(semaphore_lock); + +void __sched __down(struct semaphore * sem) +{ + struct task_struct *tsk = current; + DECLARE_WAITQUEUE(wait, tsk); + tsk->state = TASK_UNINTERRUPTIBLE; + add_wait_queue_exclusive(&sem->wait, &wait); + + spin_lock_irq(&semaphore_lock); + sem->sleepers++; + for (;;) { + int sleepers = sem->sleepers; + + /* + * Add "everybody else" into it. They aren't + * playing, because we own the spinlock. + */ + if (!atomic_add_negative(sleepers - 1, &sem->count)) { + sem->sleepers = 0; + break; + } + sem->sleepers = 1; /* us - see -1 above */ + spin_unlock_irq(&semaphore_lock); + + schedule(); + tsk->state = TASK_UNINTERRUPTIBLE; + spin_lock_irq(&semaphore_lock); + } + spin_unlock_irq(&semaphore_lock); + remove_wait_queue(&sem->wait, &wait); + tsk->state = TASK_RUNNING; + wake_up(&sem->wait); +} + +int __sched __down_interruptible(struct semaphore * sem) +{ + int retval = 0; + struct task_struct *tsk = current; + DECLARE_WAITQUEUE(wait, tsk); + tsk->state = TASK_INTERRUPTIBLE; + add_wait_queue_exclusive(&sem->wait, &wait); + + spin_lock_irq(&semaphore_lock); + 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. The + * "-1" is because we're still hoping to get + * the lock. + */ + if (!atomic_add_negative(sleepers - 1, &sem->count)) { + sem->sleepers = 0; + break; + } + sem->sleepers = 1; /* us - see -1 above */ + spin_unlock_irq(&semaphore_lock); + + schedule(); + tsk->state = TASK_INTERRUPTIBLE; + spin_lock_irq(&semaphore_lock); + } + spin_unlock_irq(&semaphore_lock); + tsk->state = TASK_RUNNING; + remove_wait_queue(&sem->wait, &wait); + wake_up(&sem->wait); + 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(&semaphore_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. + */ + if (!atomic_add_negative(sleepers, &sem->count)) + wake_up(&sem->wait); + + spin_unlock_irqrestore(&semaphore_lock, flags); + return 1; +} |