/* * PowerPC-specific semaphore code. * * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu> * * 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/sched.h> #include <linux/init.h> #include <asm/atomic.h> #include <asm/semaphore.h> #include <asm/errno.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; */ static inline int __sem_update_count(struct semaphore *sem, int incr) { int old_count, tmp; __asm__ __volatile__("\n" "1: lwarx %0,0,%3\n" " srawi %1,%0,31\n" " andc %1,%0,%1\n" " add %1,%1,%4\n" PPC405_ERR77(0,%3) " stwcx. %1,0,%3\n" " bne 1b" : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count) : "r" (&sem->count), "r" (incr), "m" (sem->count) : "cc"); 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); } /* * 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); tsk->state = TASK_UNINTERRUPTIBLE; add_wait_queue_exclusive(&sem->wait, &wait); smp_wmb(); /* * 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(); tsk->state = TASK_UNINTERRUPTIBLE; } remove_wait_queue(&sem->wait, &wait); tsk->state = 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); } 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); smp_wmb(); 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(); tsk->state = TASK_INTERRUPTIBLE; } tsk->state = TASK_RUNNING; remove_wait_queue(&sem->wait, &wait); wake_up(&sem->wait); return retval; }