Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* |
| 2 | * linux/arch/m32r/semaphore.c |
| 3 | * orig : i386 2.6.4 |
| 4 | * |
| 5 | * M32R semaphore implementation. |
| 6 | * |
| 7 | * Copyright (c) 2002 - 2004 Hitoshi Yamamoto |
| 8 | */ |
| 9 | |
| 10 | /* |
| 11 | * i386 semaphore implementation. |
| 12 | * |
| 13 | * (C) Copyright 1999 Linus Torvalds |
| 14 | * |
| 15 | * Portions Copyright 1999 Red Hat, Inc. |
| 16 | * |
| 17 | * This program is free software; you can redistribute it and/or |
| 18 | * modify it under the terms of the GNU General Public License |
| 19 | * as published by the Free Software Foundation; either version |
| 20 | * 2 of the License, or (at your option) any later version. |
| 21 | * |
| 22 | * rw semaphores implemented November 1999 by Benjamin LaHaise <bcrl@kvack.org> |
| 23 | */ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 24 | #include <linux/sched.h> |
| 25 | #include <linux/err.h> |
| 26 | #include <linux/init.h> |
| 27 | #include <asm/semaphore.h> |
| 28 | |
| 29 | /* |
| 30 | * Semaphores are implemented using a two-way counter: |
| 31 | * The "count" variable is decremented for each process |
| 32 | * that tries to acquire the semaphore, while the "sleeping" |
| 33 | * variable is a count of such acquires. |
| 34 | * |
| 35 | * Notably, the inline "up()" and "down()" functions can |
| 36 | * efficiently test if they need to do any extra work (up |
| 37 | * needs to do something only if count was negative before |
| 38 | * the increment operation. |
| 39 | * |
| 40 | * "sleeping" and the contention routine ordering is protected |
| 41 | * by the spinlock in the semaphore's waitqueue head. |
| 42 | * |
| 43 | * Note that these functions are only called when there is |
| 44 | * contention on the lock, and as such all this is the |
| 45 | * "non-critical" part of the whole semaphore business. The |
| 46 | * critical part is the inline stuff in <asm/semaphore.h> |
| 47 | * where we want to avoid any extra jumps and calls. |
| 48 | */ |
| 49 | |
| 50 | /* |
| 51 | * Logic: |
| 52 | * - only on a boundary condition do we need to care. When we go |
| 53 | * from a negative count to a non-negative, we wake people up. |
| 54 | * - when we go from a non-negative count to a negative do we |
| 55 | * (a) synchronize with the "sleeper" count and (b) make sure |
| 56 | * that we're on the wakeup list before we synchronize so that |
| 57 | * we cannot lose wakeup events. |
| 58 | */ |
| 59 | |
| 60 | asmlinkage void __up(struct semaphore *sem) |
| 61 | { |
| 62 | wake_up(&sem->wait); |
| 63 | } |
| 64 | |
| 65 | asmlinkage void __sched __down(struct semaphore * sem) |
| 66 | { |
| 67 | struct task_struct *tsk = current; |
| 68 | DECLARE_WAITQUEUE(wait, tsk); |
| 69 | unsigned long flags; |
| 70 | |
| 71 | tsk->state = TASK_UNINTERRUPTIBLE; |
| 72 | spin_lock_irqsave(&sem->wait.lock, flags); |
| 73 | add_wait_queue_exclusive_locked(&sem->wait, &wait); |
| 74 | |
| 75 | sem->sleepers++; |
| 76 | for (;;) { |
| 77 | int sleepers = sem->sleepers; |
| 78 | |
| 79 | /* |
| 80 | * Add "everybody else" into it. They aren't |
| 81 | * playing, because we own the spinlock in |
| 82 | * the wait_queue_head. |
| 83 | */ |
| 84 | if (!atomic_add_negative(sleepers - 1, &sem->count)) { |
| 85 | sem->sleepers = 0; |
| 86 | break; |
| 87 | } |
| 88 | sem->sleepers = 1; /* us - see -1 above */ |
| 89 | spin_unlock_irqrestore(&sem->wait.lock, flags); |
| 90 | |
| 91 | schedule(); |
| 92 | |
| 93 | spin_lock_irqsave(&sem->wait.lock, flags); |
| 94 | tsk->state = TASK_UNINTERRUPTIBLE; |
| 95 | } |
| 96 | remove_wait_queue_locked(&sem->wait, &wait); |
| 97 | wake_up_locked(&sem->wait); |
| 98 | spin_unlock_irqrestore(&sem->wait.lock, flags); |
| 99 | tsk->state = TASK_RUNNING; |
| 100 | } |
| 101 | |
| 102 | asmlinkage int __sched __down_interruptible(struct semaphore * sem) |
| 103 | { |
| 104 | int retval = 0; |
| 105 | struct task_struct *tsk = current; |
| 106 | DECLARE_WAITQUEUE(wait, tsk); |
| 107 | unsigned long flags; |
| 108 | |
| 109 | tsk->state = TASK_INTERRUPTIBLE; |
| 110 | spin_lock_irqsave(&sem->wait.lock, flags); |
| 111 | add_wait_queue_exclusive_locked(&sem->wait, &wait); |
| 112 | |
| 113 | sem->sleepers++; |
| 114 | for (;;) { |
| 115 | int sleepers = sem->sleepers; |
| 116 | |
| 117 | /* |
| 118 | * With signals pending, this turns into |
| 119 | * the trylock failure case - we won't be |
| 120 | * sleeping, and we* can't get the lock as |
| 121 | * it has contention. Just correct the count |
| 122 | * and exit. |
| 123 | */ |
| 124 | if (signal_pending(current)) { |
| 125 | retval = -EINTR; |
| 126 | sem->sleepers = 0; |
| 127 | atomic_add(sleepers, &sem->count); |
| 128 | break; |
| 129 | } |
| 130 | |
| 131 | /* |
| 132 | * Add "everybody else" into it. They aren't |
| 133 | * playing, because we own the spinlock in |
| 134 | * wait_queue_head. The "-1" is because we're |
| 135 | * still hoping to get the semaphore. |
| 136 | */ |
| 137 | if (!atomic_add_negative(sleepers - 1, &sem->count)) { |
| 138 | sem->sleepers = 0; |
| 139 | break; |
| 140 | } |
| 141 | sem->sleepers = 1; /* us - see -1 above */ |
| 142 | spin_unlock_irqrestore(&sem->wait.lock, flags); |
| 143 | |
| 144 | schedule(); |
| 145 | |
| 146 | spin_lock_irqsave(&sem->wait.lock, flags); |
| 147 | tsk->state = TASK_INTERRUPTIBLE; |
| 148 | } |
| 149 | remove_wait_queue_locked(&sem->wait, &wait); |
| 150 | wake_up_locked(&sem->wait); |
| 151 | spin_unlock_irqrestore(&sem->wait.lock, flags); |
| 152 | |
| 153 | tsk->state = TASK_RUNNING; |
| 154 | return retval; |
| 155 | } |
| 156 | |
| 157 | /* |
| 158 | * Trylock failed - make sure we correct for |
| 159 | * having decremented the count. |
| 160 | * |
| 161 | * We could have done the trylock with a |
| 162 | * single "cmpxchg" without failure cases, |
| 163 | * but then it wouldn't work on a 386. |
| 164 | */ |
| 165 | asmlinkage int __down_trylock(struct semaphore * sem) |
| 166 | { |
| 167 | int sleepers; |
| 168 | unsigned long flags; |
| 169 | |
| 170 | spin_lock_irqsave(&sem->wait.lock, flags); |
| 171 | sleepers = sem->sleepers + 1; |
| 172 | sem->sleepers = 0; |
| 173 | |
| 174 | /* |
| 175 | * Add "everybody else" and us into it. They aren't |
| 176 | * playing, because we own the spinlock in the |
| 177 | * wait_queue_head. |
| 178 | */ |
| 179 | if (!atomic_add_negative(sleepers, &sem->count)) { |
| 180 | wake_up_locked(&sem->wait); |
| 181 | } |
| 182 | |
| 183 | spin_unlock_irqrestore(&sem->wait.lock, flags); |
| 184 | return 1; |
| 185 | } |