Chris Zankel | 5a0015d | 2005-06-23 22:01:16 -0700 | [diff] [blame] | 1 | /* |
| 2 | * arch/xtensa/kernel/semaphore.c |
| 3 | * |
| 4 | * Generic semaphore code. Buyer beware. Do your own specific changes |
| 5 | * in <asm/semaphore-helper.h> |
| 6 | * |
| 7 | * This file is subject to the terms and conditions of the GNU General Public |
| 8 | * License. See the file "COPYING" in the main directory of this archive |
| 9 | * for more details. |
| 10 | * |
| 11 | * Copyright (C) 2001 - 2005 Tensilica Inc. |
| 12 | * |
| 13 | * Joe Taylor <joe@tensilica.com, joetylr@yahoo.com> |
| 14 | * Chris Zankel <chris@zankel.net> |
| 15 | * Marc Gauthier<marc@tensilica.com, marc@alumni.uwaterloo.ca> |
| 16 | * Kevin Chea |
| 17 | */ |
| 18 | |
| 19 | #include <linux/sched.h> |
| 20 | #include <linux/wait.h> |
| 21 | #include <linux/init.h> |
| 22 | #include <asm/semaphore.h> |
| 23 | #include <asm/errno.h> |
| 24 | |
| 25 | /* |
| 26 | * These two _must_ execute atomically wrt each other. |
| 27 | */ |
| 28 | |
| 29 | static __inline__ void wake_one_more(struct semaphore * sem) |
| 30 | { |
| 31 | atomic_inc((atomic_t *)&sem->sleepers); |
| 32 | } |
| 33 | |
| 34 | static __inline__ int waking_non_zero(struct semaphore *sem) |
| 35 | { |
| 36 | unsigned long flags; |
| 37 | int ret = 0; |
| 38 | |
| 39 | spin_lock_irqsave(&semaphore_wake_lock, flags); |
| 40 | if (sem->sleepers > 0) { |
| 41 | sem->sleepers--; |
| 42 | ret = 1; |
| 43 | } |
| 44 | spin_unlock_irqrestore(&semaphore_wake_lock, flags); |
| 45 | return ret; |
| 46 | } |
| 47 | |
| 48 | /* |
| 49 | * waking_non_zero_interruptible: |
| 50 | * 1 got the lock |
| 51 | * 0 go to sleep |
| 52 | * -EINTR interrupted |
| 53 | * |
| 54 | * We must undo the sem->count down_interruptible() increment while we are |
| 55 | * protected by the spinlock in order to make atomic this atomic_inc() with the |
| 56 | * atomic_read() in wake_one_more(), otherwise we can race. -arca |
| 57 | */ |
| 58 | |
| 59 | static __inline__ int waking_non_zero_interruptible(struct semaphore *sem, |
| 60 | struct task_struct *tsk) |
| 61 | { |
| 62 | unsigned long flags; |
| 63 | int ret = 0; |
| 64 | |
| 65 | spin_lock_irqsave(&semaphore_wake_lock, flags); |
| 66 | if (sem->sleepers > 0) { |
| 67 | sem->sleepers--; |
| 68 | ret = 1; |
| 69 | } else if (signal_pending(tsk)) { |
| 70 | atomic_inc(&sem->count); |
| 71 | ret = -EINTR; |
| 72 | } |
| 73 | spin_unlock_irqrestore(&semaphore_wake_lock, flags); |
| 74 | return ret; |
| 75 | } |
| 76 | |
| 77 | /* |
| 78 | * waking_non_zero_trylock: |
| 79 | * 1 failed to lock |
| 80 | * 0 got the lock |
| 81 | * |
| 82 | * We must undo the sem->count down_trylock() increment while we are |
| 83 | * protected by the spinlock in order to make atomic this atomic_inc() with the |
| 84 | * atomic_read() in wake_one_more(), otherwise we can race. -arca |
| 85 | */ |
| 86 | |
| 87 | static __inline__ int waking_non_zero_trylock(struct semaphore *sem) |
| 88 | { |
| 89 | unsigned long flags; |
| 90 | int ret = 1; |
| 91 | |
| 92 | spin_lock_irqsave(&semaphore_wake_lock, flags); |
| 93 | if (sem->sleepers <= 0) |
| 94 | atomic_inc(&sem->count); |
| 95 | else { |
| 96 | sem->sleepers--; |
| 97 | ret = 0; |
| 98 | } |
| 99 | spin_unlock_irqrestore(&semaphore_wake_lock, flags); |
| 100 | return ret; |
| 101 | } |
| 102 | |
| 103 | spinlock_t semaphore_wake_lock; |
| 104 | |
| 105 | /* |
| 106 | * Semaphores are implemented using a two-way counter: |
| 107 | * The "count" variable is decremented for each process |
| 108 | * that tries to sleep, while the "waking" variable is |
| 109 | * incremented when the "up()" code goes to wake up waiting |
| 110 | * processes. |
| 111 | * |
| 112 | * Notably, the inline "up()" and "down()" functions can |
| 113 | * efficiently test if they need to do any extra work (up |
| 114 | * needs to do something only if count was negative before |
| 115 | * the increment operation. |
| 116 | * |
| 117 | * waking_non_zero() (from asm/semaphore.h) must execute |
| 118 | * atomically. |
| 119 | * |
| 120 | * When __up() is called, the count was negative before |
| 121 | * incrementing it, and we need to wake up somebody. |
| 122 | * |
| 123 | * This routine adds one to the count of processes that need to |
| 124 | * wake up and exit. ALL waiting processes actually wake up but |
| 125 | * only the one that gets to the "waking" field first will gate |
| 126 | * through and acquire the semaphore. The others will go back |
| 127 | * to sleep. |
| 128 | * |
| 129 | * Note that these functions are only called when there is |
| 130 | * contention on the lock, and as such all this is the |
| 131 | * "non-critical" part of the whole semaphore business. The |
| 132 | * critical part is the inline stuff in <asm/semaphore.h> |
| 133 | * where we want to avoid any extra jumps and calls. |
| 134 | */ |
| 135 | |
| 136 | void __up(struct semaphore *sem) |
| 137 | { |
| 138 | wake_one_more(sem); |
| 139 | wake_up(&sem->wait); |
| 140 | } |
| 141 | |
| 142 | /* |
| 143 | * Perform the "down" function. Return zero for semaphore acquired, |
| 144 | * return negative for signalled out of the function. |
| 145 | * |
| 146 | * If called from __down, the return is ignored and the wait loop is |
| 147 | * not interruptible. This means that a task waiting on a semaphore |
| 148 | * using "down()" cannot be killed until someone does an "up()" on |
| 149 | * the semaphore. |
| 150 | * |
| 151 | * If called from __down_interruptible, the return value gets checked |
| 152 | * upon return. If the return value is negative then the task continues |
| 153 | * with the negative value in the return register (it can be tested by |
| 154 | * the caller). |
| 155 | * |
| 156 | * Either form may be used in conjunction with "up()". |
| 157 | * |
| 158 | */ |
| 159 | |
| 160 | #define DOWN_VAR \ |
| 161 | struct task_struct *tsk = current; \ |
| 162 | wait_queue_t wait; \ |
| 163 | init_waitqueue_entry(&wait, tsk); |
| 164 | |
| 165 | #define DOWN_HEAD(task_state) \ |
| 166 | \ |
| 167 | \ |
| 168 | tsk->state = (task_state); \ |
| 169 | add_wait_queue(&sem->wait, &wait); \ |
| 170 | \ |
| 171 | /* \ |
| 172 | * Ok, we're set up. sem->count is known to be less than zero \ |
| 173 | * so we must wait. \ |
| 174 | * \ |
| 175 | * We can let go the lock for purposes of waiting. \ |
| 176 | * We re-acquire it after awaking so as to protect \ |
| 177 | * all semaphore operations. \ |
| 178 | * \ |
| 179 | * If "up()" is called before we call waking_non_zero() then \ |
| 180 | * we will catch it right away. If it is called later then \ |
| 181 | * we will have to go through a wakeup cycle to catch it. \ |
| 182 | * \ |
| 183 | * Multiple waiters contend for the semaphore lock to see \ |
| 184 | * who gets to gate through and who has to wait some more. \ |
| 185 | */ \ |
| 186 | for (;;) { |
| 187 | |
| 188 | #define DOWN_TAIL(task_state) \ |
| 189 | tsk->state = (task_state); \ |
| 190 | } \ |
| 191 | tsk->state = TASK_RUNNING; \ |
| 192 | remove_wait_queue(&sem->wait, &wait); |
| 193 | |
| 194 | void __sched __down(struct semaphore * sem) |
| 195 | { |
| 196 | DOWN_VAR |
| 197 | DOWN_HEAD(TASK_UNINTERRUPTIBLE) |
| 198 | if (waking_non_zero(sem)) |
| 199 | break; |
| 200 | schedule(); |
| 201 | DOWN_TAIL(TASK_UNINTERRUPTIBLE) |
| 202 | } |
| 203 | |
| 204 | int __sched __down_interruptible(struct semaphore * sem) |
| 205 | { |
| 206 | int ret = 0; |
| 207 | DOWN_VAR |
| 208 | DOWN_HEAD(TASK_INTERRUPTIBLE) |
| 209 | |
| 210 | ret = waking_non_zero_interruptible(sem, tsk); |
| 211 | if (ret) |
| 212 | { |
| 213 | if (ret == 1) |
| 214 | /* ret != 0 only if we get interrupted -arca */ |
| 215 | ret = 0; |
| 216 | break; |
| 217 | } |
| 218 | schedule(); |
| 219 | DOWN_TAIL(TASK_INTERRUPTIBLE) |
| 220 | return ret; |
| 221 | } |
| 222 | |
| 223 | int __down_trylock(struct semaphore * sem) |
| 224 | { |
| 225 | return waking_non_zero_trylock(sem); |
| 226 | } |