Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mattst88...
[linux-2.6-microblaze.git] / include / linux / swait.h
1 /* SPDX-License-Identifier: GPL-2.0 */
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>
8 #include <asm/current.h>
9
10 /*
11  * Simple wait queues
12  *
13  * While these are very similar to regular wait queues (wait.h) the most
14  * important difference is that the simple waitqueue allows for deterministic
15  * behaviour -- IOW it has strictly bounded IRQ and lock hold times.
16  *
17  * Mainly, this is accomplished by two things. Firstly not allowing swake_up_all
18  * from IRQ disabled, and dropping the lock upon every wakeup, giving a higher
19  * priority task a chance to run.
20  *
21  * Secondly, we had to drop a fair number of features of the other waitqueue
22  * code; notably:
23  *
24  *  - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;
25  *    all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
26  *    sleeper state.
27  *
28  *  - the exclusive mode; because this requires preserving the list order
29  *    and this is hard.
30  *
31  *  - custom wake callback functions; because you cannot give any guarantees
32  *    about random code. This also allows swait to be used in RT, such that
33  *    raw spinlock can be used for the swait queue head.
34  *
35  * As a side effect of these; the data structures are slimmer albeit more ad-hoc.
36  * For all the above, note that simple wait queues should _only_ be used under
37  * very specific realtime constraints -- it is best to stick with the regular
38  * wait queues in most cases.
39  */
40
41 struct task_struct;
42
43 struct swait_queue_head {
44         raw_spinlock_t          lock;
45         struct list_head        task_list;
46 };
47
48 struct swait_queue {
49         struct task_struct      *task;
50         struct list_head        task_list;
51 };
52
53 #define __SWAITQUEUE_INITIALIZER(name) {                                \
54         .task           = current,                                      \
55         .task_list      = LIST_HEAD_INIT((name).task_list),             \
56 }
57
58 #define DECLARE_SWAITQUEUE(name)                                        \
59         struct swait_queue name = __SWAITQUEUE_INITIALIZER(name)
60
61 #define __SWAIT_QUEUE_HEAD_INITIALIZER(name) {                          \
62         .lock           = __RAW_SPIN_LOCK_UNLOCKED(name.lock),          \
63         .task_list      = LIST_HEAD_INIT((name).task_list),             \
64 }
65
66 #define DECLARE_SWAIT_QUEUE_HEAD(name)                                  \
67         struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name)
68
69 extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name,
70                                     struct lock_class_key *key);
71
72 #define init_swait_queue_head(q)                                \
73         do {                                                    \
74                 static struct lock_class_key __key;             \
75                 __init_swait_queue_head((q), #q, &__key);       \
76         } while (0)
77
78 #ifdef CONFIG_LOCKDEP
79 # define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)                  \
80         ({ init_swait_queue_head(&name); name; })
81 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)                 \
82         struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)
83 #else
84 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)                 \
85         DECLARE_SWAIT_QUEUE_HEAD(name)
86 #endif
87
88 /**
89  * swait_active -- locklessly test for waiters on the queue
90  * @wq: the waitqueue to test for waiters
91  *
92  * returns true if the wait list is not empty
93  *
94  * NOTE: this function is lockless and requires care, incorrect usage _will_
95  * lead to sporadic and non-obvious failure.
96  *
97  * NOTE2: this function has the same above implications as regular waitqueues.
98  *
99  * Use either while holding swait_queue_head::lock or when used for wakeups
100  * with an extra smp_mb() like:
101  *
102  *      CPU0 - waker                    CPU1 - waiter
103  *
104  *                                      for (;;) {
105  *      @cond = true;                     prepare_to_swait(&wq_head, &wait, state);
106  *      smp_mb();                         // smp_mb() from set_current_state()
107  *      if (swait_active(wq_head))        if (@cond)
108  *        wake_up(wq_head);                      break;
109  *                                        schedule();
110  *                                      }
111  *                                      finish_swait(&wq_head, &wait);
112  *
113  * Because without the explicit smp_mb() it's possible for the
114  * swait_active() load to get hoisted over the @cond store such that we'll
115  * observe an empty wait list while the waiter might not observe @cond.
116  * This, in turn, can trigger missing wakeups.
117  *
118  * Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
119  * which (when the lock is uncontended) are of roughly equal cost.
120  */
121 static inline int swait_active(struct swait_queue_head *wq)
122 {
123         return !list_empty(&wq->task_list);
124 }
125
126 /**
127  * swq_has_sleeper - check if there are any waiting processes
128  * @wq: the waitqueue to test for waiters
129  *
130  * Returns true if @wq has waiting processes
131  *
132  * Please refer to the comment for swait_active.
133  */
134 static inline bool swq_has_sleeper(struct swait_queue_head *wq)
135 {
136         /*
137          * We need to be sure we are in sync with the list_add()
138          * modifications to the wait queue (task_list).
139          *
140          * This memory barrier should be paired with one on the
141          * waiting side.
142          */
143         smp_mb();
144         return swait_active(wq);
145 }
146
147 extern void swake_up(struct swait_queue_head *q);
148 extern void swake_up_all(struct swait_queue_head *q);
149 extern void swake_up_locked(struct swait_queue_head *q);
150
151 extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
152 extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state);
153 extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);
154
155 extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
156 extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
157
158 /* as per ___wait_event() but for swait, therefore "exclusive == 0" */
159 #define ___swait_event(wq, condition, state, ret, cmd)                  \
160 ({                                                                      \
161         struct swait_queue __wait;                                      \
162         long __ret = ret;                                               \
163                                                                         \
164         INIT_LIST_HEAD(&__wait.task_list);                              \
165         for (;;) {                                                      \
166                 long __int = prepare_to_swait_event(&wq, &__wait, state);\
167                                                                         \
168                 if (condition)                                          \
169                         break;                                          \
170                                                                         \
171                 if (___wait_is_interruptible(state) && __int) {         \
172                         __ret = __int;                                  \
173                         break;                                          \
174                 }                                                       \
175                                                                         \
176                 cmd;                                                    \
177         }                                                               \
178         finish_swait(&wq, &__wait);                                     \
179         __ret;                                                          \
180 })
181
182 #define __swait_event(wq, condition)                                    \
183         (void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0,    \
184                             schedule())
185
186 #define swait_event(wq, condition)                                      \
187 do {                                                                    \
188         if (condition)                                                  \
189                 break;                                                  \
190         __swait_event(wq, condition);                                   \
191 } while (0)
192
193 #define __swait_event_timeout(wq, condition, timeout)                   \
194         ___swait_event(wq, ___wait_cond_timeout(condition),             \
195                       TASK_UNINTERRUPTIBLE, timeout,                    \
196                       __ret = schedule_timeout(__ret))
197
198 #define swait_event_timeout(wq, condition, timeout)                     \
199 ({                                                                      \
200         long __ret = timeout;                                           \
201         if (!___wait_cond_timeout(condition))                           \
202                 __ret = __swait_event_timeout(wq, condition, timeout);  \
203         __ret;                                                          \
204 })
205
206 #define __swait_event_interruptible(wq, condition)                      \
207         ___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0,            \
208                       schedule())
209
210 #define swait_event_interruptible(wq, condition)                        \
211 ({                                                                      \
212         int __ret = 0;                                                  \
213         if (!(condition))                                               \
214                 __ret = __swait_event_interruptible(wq, condition);     \
215         __ret;                                                          \
216 })
217
218 #define __swait_event_interruptible_timeout(wq, condition, timeout)     \
219         ___swait_event(wq, ___wait_cond_timeout(condition),             \
220                       TASK_INTERRUPTIBLE, timeout,                      \
221                       __ret = schedule_timeout(__ret))
222
223 #define swait_event_interruptible_timeout(wq, condition, timeout)       \
224 ({                                                                      \
225         long __ret = timeout;                                           \
226         if (!___wait_cond_timeout(condition))                           \
227                 __ret = __swait_event_interruptible_timeout(wq,         \
228                                                 condition, timeout);    \
229         __ret;                                                          \
230 })
231
232 #define __swait_event_idle(wq, condition)                               \
233         (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule())
234
235 /**
236  * swait_event_idle - wait without system load contribution
237  * @wq: the waitqueue to wait on
238  * @condition: a C expression for the event to wait for
239  *
240  * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
241  * true. The @condition is checked each time the waitqueue @wq is woken up.
242  *
243  * This function is mostly used when a kthread or workqueue waits for some
244  * condition and doesn't want to contribute to system load. Signals are
245  * ignored.
246  */
247 #define swait_event_idle(wq, condition)                                 \
248 do {                                                                    \
249         if (condition)                                                  \
250                 break;                                                  \
251         __swait_event_idle(wq, condition);                              \
252 } while (0)
253
254 #define __swait_event_idle_timeout(wq, condition, timeout)              \
255         ___swait_event(wq, ___wait_cond_timeout(condition),             \
256                        TASK_IDLE, timeout,                              \
257                        __ret = schedule_timeout(__ret))
258
259 /**
260  * swait_event_idle_timeout - wait up to timeout without load contribution
261  * @wq: the waitqueue to wait on
262  * @condition: a C expression for the event to wait for
263  * @timeout: timeout at which we'll give up in jiffies
264  *
265  * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
266  * true. The @condition is checked each time the waitqueue @wq is woken up.
267  *
268  * This function is mostly used when a kthread or workqueue waits for some
269  * condition and doesn't want to contribute to system load. Signals are
270  * ignored.
271  *
272  * Returns:
273  * 0 if the @condition evaluated to %false after the @timeout elapsed,
274  * 1 if the @condition evaluated to %true after the @timeout elapsed,
275  * or the remaining jiffies (at least 1) if the @condition evaluated
276  * to %true before the @timeout elapsed.
277  */
278 #define swait_event_idle_timeout(wq, condition, timeout)                \
279 ({                                                                      \
280         long __ret = timeout;                                           \
281         if (!___wait_cond_timeout(condition))                           \
282                 __ret = __swait_event_idle_timeout(wq,                  \
283                                                    condition, timeout); \
284         __ret;                                                          \
285 })
286
287 #endif /* _LINUX_SWAIT_H */