1 #ifndef _LINUX_SWAIT_H 2 #define _LINUX_SWAIT_H 3 4 #include <linux/list.h> 5 #include <linux/stddef.h> 6 #include <linux/spinlock.h> 7 #include <asm/current.h> 8 9 /* 10 * Simple wait queues 11 * 12 * While these are very similar to the other/complex wait queues (wait.h) the 13 * most important difference is that the simple waitqueue allows for 14 * deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold 15 * times. 16 * 17 * In order to make this so, we had to drop a fair number of features of the 18 * other waitqueue code; notably: 19 * 20 * - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue; 21 * all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right 22 * sleeper state. 23 * 24 * - the exclusive mode; because this requires preserving the list order 25 * and this is hard. 26 * 27 * - custom wake functions; because you cannot give any guarantees about 28 * random code. 29 * 30 * As a side effect of this; the data structures are slimmer. 31 * 32 * One would recommend using this wait queue where possible. 33 */ 34 35 struct task_struct; 36 37 struct swait_queue_head { 38 raw_spinlock_t lock; 39 struct list_head task_list; 40 }; 41 42 struct swait_queue { 43 struct task_struct *task; 44 struct list_head task_list; 45 }; 46 47 #define __SWAITQUEUE_INITIALIZER(name) { \ 48 .task = current, \ 49 .task_list = LIST_HEAD_INIT((name).task_list), \ 50 } 51 52 #define DECLARE_SWAITQUEUE(name) \ 53 struct swait_queue name = __SWAITQUEUE_INITIALIZER(name) 54 55 #define __SWAIT_QUEUE_HEAD_INITIALIZER(name) { \ 56 .lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \ 57 .task_list = LIST_HEAD_INIT((name).task_list), \ 58 } 59 60 #define DECLARE_SWAIT_QUEUE_HEAD(name) \ 61 struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name) 62 63 extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name, 64 struct lock_class_key *key); 65 66 #define init_swait_queue_head(q) \ 67 do { \ 68 static struct lock_class_key __key; \ 69 __init_swait_queue_head((q), #q, &__key); \ 70 } while (0) 71 72 #ifdef CONFIG_LOCKDEP 73 # define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) \ 74 ({ init_swait_queue_head(&name); name; }) 75 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \ 76 struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) 77 #else 78 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \ 79 DECLARE_SWAIT_QUEUE_HEAD(name) 80 #endif 81 82 /** 83 * swait_active -- locklessly test for waiters on the queue 84 * @wq: the waitqueue to test for waiters 85 * 86 * returns true if the wait list is not empty 87 * 88 * NOTE: this function is lockless and requires care, incorrect usage _will_ 89 * lead to sporadic and non-obvious failure. 90 * 91 * NOTE2: this function has the same above implications as regular waitqueues. 92 * 93 * Use either while holding swait_queue_head::lock or when used for wakeups 94 * with an extra smp_mb() like: 95 * 96 * CPU0 - waker CPU1 - waiter 97 * 98 * for (;;) { 99 * @cond = true; prepare_to_swait(&wq_head, &wait, state); 100 * smp_mb(); // smp_mb() from set_current_state() 101 * if (swait_active(wq_head)) if (@cond) 102 * wake_up(wq_head); break; 103 * schedule(); 104 * } 105 * finish_swait(&wq_head, &wait); 106 * 107 * Because without the explicit smp_mb() it's possible for the 108 * swait_active() load to get hoisted over the @cond store such that we'll 109 * observe an empty wait list while the waiter might not observe @cond. 110 * This, in turn, can trigger missing wakeups. 111 * 112 * Also note that this 'optimization' trades a spin_lock() for an smp_mb(), 113 * which (when the lock is uncontended) are of roughly equal cost. 114 */ 115 static inline int swait_active(struct swait_queue_head *wq) 116 { 117 return !list_empty(&wq->task_list); 118 } 119 120 /** 121 * swq_has_sleeper - check if there are any waiting processes 122 * @wq: the waitqueue to test for waiters 123 * 124 * Returns true if @wq has waiting processes 125 * 126 * Please refer to the comment for swait_active. 127 */ 128 static inline bool swq_has_sleeper(struct swait_queue_head *wq) 129 { 130 /* 131 * We need to be sure we are in sync with the list_add() 132 * modifications to the wait queue (task_list). 133 * 134 * This memory barrier should be paired with one on the 135 * waiting side. 136 */ 137 smp_mb(); 138 return swait_active(wq); 139 } 140 141 extern void swake_up(struct swait_queue_head *q); 142 extern void swake_up_all(struct swait_queue_head *q); 143 extern void swake_up_locked(struct swait_queue_head *q); 144 145 extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait); 146 extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state); 147 extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state); 148 149 extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait); 150 extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait); 151 152 /* as per ___wait_event() but for swait, therefore "exclusive == 0" */ 153 #define ___swait_event(wq, condition, state, ret, cmd) \ 154 ({ \ 155 struct swait_queue __wait; \ 156 long __ret = ret; \ 157 \ 158 INIT_LIST_HEAD(&__wait.task_list); \ 159 for (;;) { \ 160 long __int = prepare_to_swait_event(&wq, &__wait, state);\ 161 \ 162 if (condition) \ 163 break; \ 164 \ 165 if (___wait_is_interruptible(state) && __int) { \ 166 __ret = __int; \ 167 break; \ 168 } \ 169 \ 170 cmd; \ 171 } \ 172 finish_swait(&wq, &__wait); \ 173 __ret; \ 174 }) 175 176 #define __swait_event(wq, condition) \ 177 (void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, \ 178 schedule()) 179 180 #define swait_event(wq, condition) \ 181 do { \ 182 if (condition) \ 183 break; \ 184 __swait_event(wq, condition); \ 185 } while (0) 186 187 #define __swait_event_timeout(wq, condition, timeout) \ 188 ___swait_event(wq, ___wait_cond_timeout(condition), \ 189 TASK_UNINTERRUPTIBLE, timeout, \ 190 __ret = schedule_timeout(__ret)) 191 192 #define swait_event_timeout(wq, condition, timeout) \ 193 ({ \ 194 long __ret = timeout; \ 195 if (!___wait_cond_timeout(condition)) \ 196 __ret = __swait_event_timeout(wq, condition, timeout); \ 197 __ret; \ 198 }) 199 200 #define __swait_event_interruptible(wq, condition) \ 201 ___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0, \ 202 schedule()) 203 204 #define swait_event_interruptible(wq, condition) \ 205 ({ \ 206 int __ret = 0; \ 207 if (!(condition)) \ 208 __ret = __swait_event_interruptible(wq, condition); \ 209 __ret; \ 210 }) 211 212 #define __swait_event_interruptible_timeout(wq, condition, timeout) \ 213 ___swait_event(wq, ___wait_cond_timeout(condition), \ 214 TASK_INTERRUPTIBLE, timeout, \ 215 __ret = schedule_timeout(__ret)) 216 217 #define swait_event_interruptible_timeout(wq, condition, timeout) \ 218 ({ \ 219 long __ret = timeout; \ 220 if (!___wait_cond_timeout(condition)) \ 221 __ret = __swait_event_interruptible_timeout(wq, \ 222 condition, timeout); \ 223 __ret; \ 224 }) 225 226 #define __swait_event_idle(wq, condition) \ 227 (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule()) 228 229 /** 230 * swait_event_idle - wait without system load contribution 231 * @wq: the waitqueue to wait on 232 * @condition: a C expression for the event to wait for 233 * 234 * The process is put to sleep (TASK_IDLE) until the @condition evaluates to 235 * true. The @condition is checked each time the waitqueue @wq is woken up. 236 * 237 * This function is mostly used when a kthread or workqueue waits for some 238 * condition and doesn't want to contribute to system load. Signals are 239 * ignored. 240 */ 241 #define swait_event_idle(wq, condition) \ 242 do { \ 243 if (condition) \ 244 break; \ 245 __swait_event_idle(wq, condition); \ 246 } while (0) 247 248 #define __swait_event_idle_timeout(wq, condition, timeout) \ 249 ___swait_event(wq, ___wait_cond_timeout(condition), \ 250 TASK_IDLE, timeout, \ 251 __ret = schedule_timeout(__ret)) 252 253 /** 254 * swait_event_idle_timeout - wait up to timeout without load contribution 255 * @wq: the waitqueue to wait on 256 * @condition: a C expression for the event to wait for 257 * @timeout: timeout at which we'll give up in jiffies 258 * 259 * The process is put to sleep (TASK_IDLE) until the @condition evaluates to 260 * true. The @condition is checked each time the waitqueue @wq is woken up. 261 * 262 * This function is mostly used when a kthread or workqueue waits for some 263 * condition and doesn't want to contribute to system load. Signals are 264 * ignored. 265 * 266 * Returns: 267 * 0 if the @condition evaluated to %false after the @timeout elapsed, 268 * 1 if the @condition evaluated to %true after the @timeout elapsed, 269 * or the remaining jiffies (at least 1) if the @condition evaluated 270 * to %true before the @timeout elapsed. 271 */ 272 #define swait_event_idle_timeout(wq, condition, timeout) \ 273 ({ \ 274 long __ret = timeout; \ 275 if (!___wait_cond_timeout(condition)) \ 276 __ret = __swait_event_idle_timeout(wq, \ 277 condition, timeout); \ 278 __ret; \ 279 }) 280 281 #endif /* _LINUX_SWAIT_H */ 282