diff options
Diffstat (limited to 'arch/mips/kernel/semaphore.c')
| -rw-r--r-- | arch/mips/kernel/semaphore.c | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/arch/mips/kernel/semaphore.c b/arch/mips/kernel/semaphore.c new file mode 100644 index 00000000000..9c40fe5a8e8 --- /dev/null +++ b/arch/mips/kernel/semaphore.c @@ -0,0 +1,164 @@ +/* + * MIPS-specific semaphore code. + * + * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu> + * Copyright (C) 2004 Ralf Baechle <ralf@linux-mips.org> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + * + * April 2001 - Reworked by Paul Mackerras <paulus@samba.org> + * to eliminate the SMP races in the old version between the updates + * of `count' and `waking'. Now we use negative `count' values to + * indicate that some process(es) are waiting for the semaphore. + */ + +#include <linux/module.h> +#include <linux/sched.h> +#include <linux/init.h> +#include <asm/atomic.h> +#include <asm/cpu-features.h> +#include <asm/errno.h> +#include <asm/semaphore.h> +#include <asm/war.h> +/* + * Atomically update sem->count. + * This does the equivalent of the following: + * + * old_count = sem->count; + * tmp = MAX(old_count, 0) + incr; + * sem->count = tmp; + * return old_count; + * + * On machines without lld/scd we need a spinlock to make the manipulation of + * sem->count and sem->waking atomic. Scalability isn't an issue because + * this lock is used on UP only so it's just an empty variable. + */ +static inline int __sem_update_count(struct semaphore *sem, int incr) +{ + int old_count, tmp; + + if (cpu_has_llsc && R10000_LLSC_WAR) { + __asm__ __volatile__( + "1: ll %0, %2 \n" + " sra %1, %0, 31 \n" + " not %1 \n" + " and %1, %0, %1 \n" + " add %1, %1, %3 \n" + " sc %1, %2 \n" + " beqzl %1, 1b \n" + : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count) + : "r" (incr), "m" (sem->count)); + } else if (cpu_has_llsc) { + __asm__ __volatile__( + "1: ll %0, %2 \n" + " sra %1, %0, 31 \n" + " not %1 \n" + " and %1, %0, %1 \n" + " add %1, %1, %3 \n" + " sc %1, %2 \n" + " beqz %1, 1b \n" + : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count) + : "r" (incr), "m" (sem->count)); + } else { + static DEFINE_SPINLOCK(semaphore_lock); + unsigned long flags; + + spin_lock_irqsave(&semaphore_lock, flags); + old_count = atomic_read(&sem->count); + tmp = max_t(int, old_count, 0) + incr; + atomic_set(&sem->count, tmp); + spin_unlock_irqrestore(&semaphore_lock, flags); + } + + return old_count; +} + +void __up(struct semaphore *sem) +{ + /* + * Note that we incremented count in up() before we came here, + * but that was ineffective since the result was <= 0, and + * any negative value of count is equivalent to 0. + * This ends up setting count to 1, unless count is now > 0 + * (i.e. because some other cpu has called up() in the meantime), + * in which case we just increment count. + */ + __sem_update_count(sem, 1); + wake_up(&sem->wait); +} + +EXPORT_SYMBOL(__up); + +/* + * Note that when we come in to __down or __down_interruptible, + * we have already decremented count, but that decrement was + * ineffective since the result was < 0, and any negative value + * of count is equivalent to 0. + * Thus it is only when we decrement count from some value > 0 + * that we have actually got the semaphore. + */ +void __sched __down(struct semaphore *sem) +{ + struct task_struct *tsk = current; + DECLARE_WAITQUEUE(wait, tsk); + + __set_task_state(tsk, TASK_UNINTERRUPTIBLE); + add_wait_queue_exclusive(&sem->wait, &wait); + + /* + * Try to get the semaphore. If the count is > 0, then we've + * got the semaphore; we decrement count and exit the loop. + * If the count is 0 or negative, we set it to -1, indicating + * that we are asleep, and then sleep. + */ + while (__sem_update_count(sem, -1) <= 0) { + schedule(); + set_task_state(tsk, TASK_UNINTERRUPTIBLE); + } + remove_wait_queue(&sem->wait, &wait); + __set_task_state(tsk, TASK_RUNNING); + + /* + * If there are any more sleepers, wake one of them up so + * that it can either get the semaphore, or set count to -1 + * indicating that there are still processes sleeping. + */ + wake_up(&sem->wait); +} + +EXPORT_SYMBOL(__down); + +int __sched __down_interruptible(struct semaphore * sem) +{ + int retval = 0; + struct task_struct *tsk = current; + DECLARE_WAITQUEUE(wait, tsk); + + __set_task_state(tsk, TASK_INTERRUPTIBLE); + add_wait_queue_exclusive(&sem->wait, &wait); + + while (__sem_update_count(sem, -1) <= 0) { + if (signal_pending(current)) { + /* + * A signal is pending - give up trying. + * Set sem->count to 0 if it is negative, + * since we are no longer sleeping. + */ + __sem_update_count(sem, 0); + retval = -EINTR; + break; + } + schedule(); + set_task_state(tsk, TASK_INTERRUPTIBLE); + } + remove_wait_queue(&sem->wait, &wait); + __set_task_state(tsk, TASK_RUNNING); + + wake_up(&sem->wait); + return retval; +} + +EXPORT_SYMBOL(__down_interruptible); |