]>
Commit | Line | Data |
---|---|---|
b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
13b35686 PZI |
2 | #ifndef _LINUX_SWAIT_H |
3 | #define _LINUX_SWAIT_H | |
4 | ||
5 | #include <linux/list.h> | |
6 | #include <linux/stddef.h> | |
7 | #include <linux/spinlock.h> | |
a59a68fe | 8 | #include <linux/wait.h> |
13b35686 PZI |
9 | #include <asm/current.h> |
10 | ||
11 | /* | |
c5e7a7ea LT |
12 | * BROKEN wait-queues. |
13 | * | |
14 | * These "simple" wait-queues are broken garbage, and should never be | |
15 | * used. The comments below claim that they are "similar" to regular | |
16 | * wait-queues, but the semantics are actually completely different, and | |
17 | * every single user we have ever had has been buggy (or pointless). | |
18 | * | |
b3dae109 | 19 | * A "swake_up_one()" only wakes up _one_ waiter, which is not at all what |
c5e7a7ea LT |
20 | * "wake_up()" does, and has led to problems. In other cases, it has |
21 | * been fine, because there's only ever one waiter (kvm), but in that | |
22 | * case gthe whole "simple" wait-queue is just pointless to begin with, | |
23 | * since there is no "queue". Use "wake_up_process()" with a direct | |
24 | * pointer instead. | |
13b35686 | 25 | * |
88796e7e DB |
26 | * While these are very similar to regular wait queues (wait.h) the most |
27 | * important difference is that the simple waitqueue allows for deterministic | |
28 | * behaviour -- IOW it has strictly bounded IRQ and lock hold times. | |
13b35686 | 29 | * |
88796e7e DB |
30 | * Mainly, this is accomplished by two things. Firstly not allowing swake_up_all |
31 | * from IRQ disabled, and dropping the lock upon every wakeup, giving a higher | |
32 | * priority task a chance to run. | |
33 | * | |
34 | * Secondly, we had to drop a fair number of features of the other waitqueue | |
35 | * code; notably: | |
13b35686 PZI |
36 | * |
37 | * - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue; | |
38 | * all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right | |
39 | * sleeper state. | |
40 | * | |
0abf17bc PZ |
41 | * - the !exclusive mode; because that leads to O(n) wakeups, everything is |
42 | * exclusive. | |
13b35686 | 43 | * |
88796e7e DB |
44 | * - custom wake callback functions; because you cannot give any guarantees |
45 | * about random code. This also allows swait to be used in RT, such that | |
46 | * raw spinlock can be used for the swait queue head. | |
13b35686 | 47 | * |
88796e7e DB |
48 | * As a side effect of these; the data structures are slimmer albeit more ad-hoc. |
49 | * For all the above, note that simple wait queues should _only_ be used under | |
50 | * very specific realtime constraints -- it is best to stick with the regular | |
51 | * wait queues in most cases. | |
13b35686 PZI |
52 | */ |
53 | ||
54 | struct task_struct; | |
55 | ||
56 | struct swait_queue_head { | |
57 | raw_spinlock_t lock; | |
58 | struct list_head task_list; | |
59 | }; | |
60 | ||
61 | struct swait_queue { | |
62 | struct task_struct *task; | |
63 | struct list_head task_list; | |
64 | }; | |
65 | ||
66 | #define __SWAITQUEUE_INITIALIZER(name) { \ | |
67 | .task = current, \ | |
68 | .task_list = LIST_HEAD_INIT((name).task_list), \ | |
69 | } | |
70 | ||
71 | #define DECLARE_SWAITQUEUE(name) \ | |
72 | struct swait_queue name = __SWAITQUEUE_INITIALIZER(name) | |
73 | ||
74 | #define __SWAIT_QUEUE_HEAD_INITIALIZER(name) { \ | |
75 | .lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \ | |
76 | .task_list = LIST_HEAD_INIT((name).task_list), \ | |
77 | } | |
78 | ||
79 | #define DECLARE_SWAIT_QUEUE_HEAD(name) \ | |
80 | struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name) | |
81 | ||
82 | extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name, | |
83 | struct lock_class_key *key); | |
84 | ||
85 | #define init_swait_queue_head(q) \ | |
86 | do { \ | |
87 | static struct lock_class_key __key; \ | |
88 | __init_swait_queue_head((q), #q, &__key); \ | |
89 | } while (0) | |
90 | ||
91 | #ifdef CONFIG_LOCKDEP | |
92 | # define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) \ | |
93 | ({ init_swait_queue_head(&name); name; }) | |
94 | # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \ | |
95 | struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) | |
96 | #else | |
97 | # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \ | |
98 | DECLARE_SWAIT_QUEUE_HEAD(name) | |
99 | #endif | |
100 | ||
8cd641e3 DB |
101 | /** |
102 | * swait_active -- locklessly test for waiters on the queue | |
103 | * @wq: the waitqueue to test for waiters | |
104 | * | |
105 | * returns true if the wait list is not empty | |
106 | * | |
107 | * NOTE: this function is lockless and requires care, incorrect usage _will_ | |
108 | * lead to sporadic and non-obvious failure. | |
109 | * | |
110 | * NOTE2: this function has the same above implications as regular waitqueues. | |
111 | * | |
112 | * Use either while holding swait_queue_head::lock or when used for wakeups | |
113 | * with an extra smp_mb() like: | |
114 | * | |
115 | * CPU0 - waker CPU1 - waiter | |
116 | * | |
117 | * for (;;) { | |
b3dae109 | 118 | * @cond = true; prepare_to_swait_exclusive(&wq_head, &wait, state); |
8cd641e3 DB |
119 | * smp_mb(); // smp_mb() from set_current_state() |
120 | * if (swait_active(wq_head)) if (@cond) | |
121 | * wake_up(wq_head); break; | |
122 | * schedule(); | |
123 | * } | |
124 | * finish_swait(&wq_head, &wait); | |
125 | * | |
126 | * Because without the explicit smp_mb() it's possible for the | |
127 | * swait_active() load to get hoisted over the @cond store such that we'll | |
128 | * observe an empty wait list while the waiter might not observe @cond. | |
129 | * This, in turn, can trigger missing wakeups. | |
130 | * | |
131 | * Also note that this 'optimization' trades a spin_lock() for an smp_mb(), | |
132 | * which (when the lock is uncontended) are of roughly equal cost. | |
133 | */ | |
134 | static inline int swait_active(struct swait_queue_head *wq) | |
135 | { | |
136 | return !list_empty(&wq->task_list); | |
137 | } | |
138 | ||
139 | /** | |
140 | * swq_has_sleeper - check if there are any waiting processes | |
141 | * @wq: the waitqueue to test for waiters | |
142 | * | |
143 | * Returns true if @wq has waiting processes | |
144 | * | |
145 | * Please refer to the comment for swait_active. | |
146 | */ | |
147 | static inline bool swq_has_sleeper(struct swait_queue_head *wq) | |
13b35686 | 148 | { |
8cd641e3 DB |
149 | /* |
150 | * We need to be sure we are in sync with the list_add() | |
151 | * modifications to the wait queue (task_list). | |
152 | * | |
153 | * This memory barrier should be paired with one on the | |
154 | * waiting side. | |
155 | */ | |
156 | smp_mb(); | |
157 | return swait_active(wq); | |
13b35686 PZI |
158 | } |
159 | ||
b3dae109 | 160 | extern void swake_up_one(struct swait_queue_head *q); |
13b35686 PZI |
161 | extern void swake_up_all(struct swait_queue_head *q); |
162 | extern void swake_up_locked(struct swait_queue_head *q); | |
163 | ||
b3dae109 | 164 | extern void prepare_to_swait_exclusive(struct swait_queue_head *q, struct swait_queue *wait, int state); |
13b35686 PZI |
165 | extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state); |
166 | ||
167 | extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait); | |
168 | extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait); | |
169 | ||
0abf17bc | 170 | /* as per ___wait_event() but for swait, therefore "exclusive == 1" */ |
13b35686 PZI |
171 | #define ___swait_event(wq, condition, state, ret, cmd) \ |
172 | ({ \ | |
0abf17bc | 173 | __label__ __out; \ |
13b35686 PZI |
174 | struct swait_queue __wait; \ |
175 | long __ret = ret; \ | |
176 | \ | |
177 | INIT_LIST_HEAD(&__wait.task_list); \ | |
178 | for (;;) { \ | |
179 | long __int = prepare_to_swait_event(&wq, &__wait, state);\ | |
180 | \ | |
181 | if (condition) \ | |
182 | break; \ | |
183 | \ | |
184 | if (___wait_is_interruptible(state) && __int) { \ | |
185 | __ret = __int; \ | |
0abf17bc | 186 | goto __out; \ |
13b35686 PZI |
187 | } \ |
188 | \ | |
189 | cmd; \ | |
190 | } \ | |
191 | finish_swait(&wq, &__wait); \ | |
0abf17bc | 192 | __out: __ret; \ |
13b35686 PZI |
193 | }) |
194 | ||
195 | #define __swait_event(wq, condition) \ | |
196 | (void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, \ | |
197 | schedule()) | |
198 | ||
b3dae109 | 199 | #define swait_event_exclusive(wq, condition) \ |
13b35686 PZI |
200 | do { \ |
201 | if (condition) \ | |
202 | break; \ | |
203 | __swait_event(wq, condition); \ | |
204 | } while (0) | |
205 | ||
206 | #define __swait_event_timeout(wq, condition, timeout) \ | |
207 | ___swait_event(wq, ___wait_cond_timeout(condition), \ | |
208 | TASK_UNINTERRUPTIBLE, timeout, \ | |
209 | __ret = schedule_timeout(__ret)) | |
210 | ||
b3dae109 | 211 | #define swait_event_timeout_exclusive(wq, condition, timeout) \ |
13b35686 PZI |
212 | ({ \ |
213 | long __ret = timeout; \ | |
214 | if (!___wait_cond_timeout(condition)) \ | |
215 | __ret = __swait_event_timeout(wq, condition, timeout); \ | |
216 | __ret; \ | |
217 | }) | |
218 | ||
219 | #define __swait_event_interruptible(wq, condition) \ | |
220 | ___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0, \ | |
221 | schedule()) | |
222 | ||
b3dae109 | 223 | #define swait_event_interruptible_exclusive(wq, condition) \ |
13b35686 PZI |
224 | ({ \ |
225 | int __ret = 0; \ | |
226 | if (!(condition)) \ | |
227 | __ret = __swait_event_interruptible(wq, condition); \ | |
228 | __ret; \ | |
229 | }) | |
230 | ||
231 | #define __swait_event_interruptible_timeout(wq, condition, timeout) \ | |
232 | ___swait_event(wq, ___wait_cond_timeout(condition), \ | |
233 | TASK_INTERRUPTIBLE, timeout, \ | |
234 | __ret = schedule_timeout(__ret)) | |
235 | ||
b3dae109 | 236 | #define swait_event_interruptible_timeout_exclusive(wq, condition, timeout)\ |
13b35686 PZI |
237 | ({ \ |
238 | long __ret = timeout; \ | |
239 | if (!___wait_cond_timeout(condition)) \ | |
240 | __ret = __swait_event_interruptible_timeout(wq, \ | |
241 | condition, timeout); \ | |
242 | __ret; \ | |
243 | }) | |
244 | ||
352eee12 LR |
245 | #define __swait_event_idle(wq, condition) \ |
246 | (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule()) | |
247 | ||
248 | /** | |
b3dae109 | 249 | * swait_event_idle_exclusive - wait without system load contribution |
352eee12 LR |
250 | * @wq: the waitqueue to wait on |
251 | * @condition: a C expression for the event to wait for | |
252 | * | |
253 | * The process is put to sleep (TASK_IDLE) until the @condition evaluates to | |
254 | * true. The @condition is checked each time the waitqueue @wq is woken up. | |
255 | * | |
256 | * This function is mostly used when a kthread or workqueue waits for some | |
257 | * condition and doesn't want to contribute to system load. Signals are | |
258 | * ignored. | |
259 | */ | |
b3dae109 | 260 | #define swait_event_idle_exclusive(wq, condition) \ |
352eee12 LR |
261 | do { \ |
262 | if (condition) \ | |
263 | break; \ | |
264 | __swait_event_idle(wq, condition); \ | |
265 | } while (0) | |
266 | ||
267 | #define __swait_event_idle_timeout(wq, condition, timeout) \ | |
268 | ___swait_event(wq, ___wait_cond_timeout(condition), \ | |
269 | TASK_IDLE, timeout, \ | |
270 | __ret = schedule_timeout(__ret)) | |
271 | ||
272 | /** | |
b3dae109 | 273 | * swait_event_idle_timeout_exclusive - wait up to timeout without load contribution |
352eee12 LR |
274 | * @wq: the waitqueue to wait on |
275 | * @condition: a C expression for the event to wait for | |
276 | * @timeout: timeout at which we'll give up in jiffies | |
277 | * | |
278 | * The process is put to sleep (TASK_IDLE) until the @condition evaluates to | |
279 | * true. The @condition is checked each time the waitqueue @wq is woken up. | |
280 | * | |
281 | * This function is mostly used when a kthread or workqueue waits for some | |
282 | * condition and doesn't want to contribute to system load. Signals are | |
283 | * ignored. | |
284 | * | |
285 | * Returns: | |
286 | * 0 if the @condition evaluated to %false after the @timeout elapsed, | |
287 | * 1 if the @condition evaluated to %true after the @timeout elapsed, | |
288 | * or the remaining jiffies (at least 1) if the @condition evaluated | |
289 | * to %true before the @timeout elapsed. | |
290 | */ | |
b3dae109 | 291 | #define swait_event_idle_timeout_exclusive(wq, condition, timeout) \ |
352eee12 LR |
292 | ({ \ |
293 | long __ret = timeout; \ | |
294 | if (!___wait_cond_timeout(condition)) \ | |
295 | __ret = __swait_event_idle_timeout(wq, \ | |
296 | condition, timeout); \ | |
297 | __ret; \ | |
298 | }) | |
299 | ||
13b35686 | 300 | #endif /* _LINUX_SWAIT_H */ |