Paul Mackerras | 14cf11a | 2005-09-26 16:04:21 +1000 | [diff] [blame] | 1 | /* |
| 2 | * PowerPC-specific semaphore code. |
| 3 | * |
| 4 | * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu> |
| 5 | * |
| 6 | * This program is free software; you can redistribute it and/or |
| 7 | * modify it under the terms of the GNU General Public License |
| 8 | * as published by the Free Software Foundation; either version |
| 9 | * 2 of the License, or (at your option) any later version. |
| 10 | * |
| 11 | * April 2001 - Reworked by Paul Mackerras <paulus@samba.org> |
| 12 | * to eliminate the SMP races in the old version between the updates |
| 13 | * of `count' and `waking'. Now we use negative `count' values to |
| 14 | * indicate that some process(es) are waiting for the semaphore. |
| 15 | */ |
| 16 | |
| 17 | #include <linux/sched.h> |
| 18 | #include <linux/init.h> |
| 19 | #include <linux/module.h> |
| 20 | |
| 21 | #include <asm/atomic.h> |
| 22 | #include <asm/semaphore.h> |
| 23 | #include <asm/errno.h> |
| 24 | |
| 25 | /* |
| 26 | * Atomically update sem->count. |
| 27 | * This does the equivalent of the following: |
| 28 | * |
| 29 | * old_count = sem->count; |
| 30 | * tmp = MAX(old_count, 0) + incr; |
| 31 | * sem->count = tmp; |
| 32 | * return old_count; |
| 33 | */ |
| 34 | static inline int __sem_update_count(struct semaphore *sem, int incr) |
| 35 | { |
| 36 | int old_count, tmp; |
| 37 | |
| 38 | __asm__ __volatile__("\n" |
| 39 | "1: lwarx %0,0,%3\n" |
| 40 | " srawi %1,%0,31\n" |
| 41 | " andc %1,%0,%1\n" |
| 42 | " add %1,%1,%4\n" |
| 43 | PPC405_ERR77(0,%3) |
| 44 | " stwcx. %1,0,%3\n" |
| 45 | " bne 1b" |
| 46 | : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count) |
| 47 | : "r" (&sem->count), "r" (incr), "m" (sem->count) |
| 48 | : "cc"); |
| 49 | |
| 50 | return old_count; |
| 51 | } |
| 52 | |
| 53 | void __up(struct semaphore *sem) |
| 54 | { |
| 55 | /* |
| 56 | * Note that we incremented count in up() before we came here, |
| 57 | * but that was ineffective since the result was <= 0, and |
| 58 | * any negative value of count is equivalent to 0. |
| 59 | * This ends up setting count to 1, unless count is now > 0 |
| 60 | * (i.e. because some other cpu has called up() in the meantime), |
| 61 | * in which case we just increment count. |
| 62 | */ |
| 63 | __sem_update_count(sem, 1); |
| 64 | wake_up(&sem->wait); |
| 65 | } |
| 66 | EXPORT_SYMBOL(__up); |
| 67 | |
| 68 | /* |
| 69 | * Note that when we come in to __down or __down_interruptible, |
| 70 | * we have already decremented count, but that decrement was |
| 71 | * ineffective since the result was < 0, and any negative value |
| 72 | * of count is equivalent to 0. |
| 73 | * Thus it is only when we decrement count from some value > 0 |
| 74 | * that we have actually got the semaphore. |
| 75 | */ |
| 76 | void __sched __down(struct semaphore *sem) |
| 77 | { |
| 78 | struct task_struct *tsk = current; |
| 79 | DECLARE_WAITQUEUE(wait, tsk); |
| 80 | |
| 81 | __set_task_state(tsk, TASK_UNINTERRUPTIBLE); |
| 82 | add_wait_queue_exclusive(&sem->wait, &wait); |
| 83 | |
| 84 | /* |
| 85 | * Try to get the semaphore. If the count is > 0, then we've |
| 86 | * got the semaphore; we decrement count and exit the loop. |
| 87 | * If the count is 0 or negative, we set it to -1, indicating |
| 88 | * that we are asleep, and then sleep. |
| 89 | */ |
| 90 | while (__sem_update_count(sem, -1) <= 0) { |
| 91 | schedule(); |
| 92 | set_task_state(tsk, TASK_UNINTERRUPTIBLE); |
| 93 | } |
| 94 | remove_wait_queue(&sem->wait, &wait); |
| 95 | __set_task_state(tsk, TASK_RUNNING); |
| 96 | |
| 97 | /* |
| 98 | * If there are any more sleepers, wake one of them up so |
| 99 | * that it can either get the semaphore, or set count to -1 |
| 100 | * indicating that there are still processes sleeping. |
| 101 | */ |
| 102 | wake_up(&sem->wait); |
| 103 | } |
| 104 | EXPORT_SYMBOL(__down); |
| 105 | |
| 106 | int __sched __down_interruptible(struct semaphore * sem) |
| 107 | { |
| 108 | int retval = 0; |
| 109 | struct task_struct *tsk = current; |
| 110 | DECLARE_WAITQUEUE(wait, tsk); |
| 111 | |
| 112 | __set_task_state(tsk, TASK_INTERRUPTIBLE); |
| 113 | add_wait_queue_exclusive(&sem->wait, &wait); |
| 114 | |
| 115 | while (__sem_update_count(sem, -1) <= 0) { |
| 116 | if (signal_pending(current)) { |
| 117 | /* |
| 118 | * A signal is pending - give up trying. |
| 119 | * Set sem->count to 0 if it is negative, |
| 120 | * since we are no longer sleeping. |
| 121 | */ |
| 122 | __sem_update_count(sem, 0); |
| 123 | retval = -EINTR; |
| 124 | break; |
| 125 | } |
| 126 | schedule(); |
| 127 | set_task_state(tsk, TASK_INTERRUPTIBLE); |
| 128 | } |
| 129 | remove_wait_queue(&sem->wait, &wait); |
| 130 | __set_task_state(tsk, TASK_RUNNING); |
| 131 | |
| 132 | wake_up(&sem->wait); |
| 133 | return retval; |
| 134 | } |
| 135 | EXPORT_SYMBOL(__down_interruptible); |