[linux-block.git] / include / linux / swait.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_SWAIT_H
#define _LINUX_SWAIT_H

#include <linux/list.h>
#include <linux/stddef.h>
#include <linux/spinlock.h>
#include <asm/current.h>

/*
 * Simple wait queues
 *
 * While these are very similar to the other/complex wait queues (wait.h) the
 * most important difference is that the simple waitqueue allows for
 * deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold
 * times.
 *
 * In order to make this so, we had to drop a fair number of features of the
 * other waitqueue code; notably:
 *
 *  - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;
 *    all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
 *    sleeper state.
 *
 *  - the exclusive mode; because this requires preserving the list order
 *    and this is hard.
 *
 *  - custom wake functions; because you cannot give any guarantees about
 *    random code.
 *
 * As a side effect of this; the data structures are slimmer.
 *
 * One would recommend using this wait queue where possible.
 */

struct task_struct;

struct swait_queue_head {
	raw_spinlock_t		lock;
	struct list_head	task_list;
};

struct swait_queue {
	struct task_struct	*task;
	struct list_head	task_list;
};

#define __SWAITQUEUE_INITIALIZER(name) {				\
	.task		= current,					\
	.task_list	= LIST_HEAD_INIT((name).task_list),		\
}

#define DECLARE_SWAITQUEUE(name)					\
	struct swait_queue name = __SWAITQUEUE_INITIALIZER(name)

#define __SWAIT_QUEUE_HEAD_INITIALIZER(name) {				\
	.lock		= __RAW_SPIN_LOCK_UNLOCKED(name.lock),		\
	.task_list	= LIST_HEAD_INIT((name).task_list),		\
}

#define DECLARE_SWAIT_QUEUE_HEAD(name)					\
	struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name)

extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name,
				    struct lock_class_key *key);

#define init_swait_queue_head(q)				\
	do {							\
		static struct lock_class_key __key;		\
		__init_swait_queue_head((q), #q, &__key);	\
	} while (0)

#ifdef CONFIG_LOCKDEP
# define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)			\
	({ init_swait_queue_head(&name); name; })
# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)			\
	struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)
#else
# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)			\
	DECLARE_SWAIT_QUEUE_HEAD(name)
#endif

/**
 * swait_active -- locklessly test for waiters on the queue
 * @wq: the waitqueue to test for waiters
 *
 * returns true if the wait list is not empty
 *
 * NOTE: this function is lockless and requires care, incorrect usage _will_
 * lead to sporadic and non-obvious failure.
 *
 * NOTE2: this function has the same above implications as regular waitqueues.
 *
 * Use either while holding swait_queue_head::lock or when used for wakeups
 * with an extra smp_mb() like:
 *
 *      CPU0 - waker                    CPU1 - waiter
 *
 *                                      for (;;) {
 *      @cond = true;                     prepare_to_swait(&wq_head, &wait, state);
 *      smp_mb();                         // smp_mb() from set_current_state()
 *      if (swait_active(wq_head))        if (@cond)
 *        wake_up(wq_head);                      break;
 *                                        schedule();
 *                                      }
 *                                      finish_swait(&wq_head, &wait);
 *
 * Because without the explicit smp_mb() it's possible for the
 * swait_active() load to get hoisted over the @cond store such that we'll
 * observe an empty wait list while the waiter might not observe @cond.
 * This, in turn, can trigger missing wakeups.
 *
 * Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
 * which (when the lock is uncontended) are of roughly equal cost.
 */
static inline int swait_active(struct swait_queue_head *wq)
{
	return !list_empty(&wq->task_list);
}

/**
 * swq_has_sleeper - check if there are any waiting processes
 * @wq: the waitqueue to test for waiters
 *
 * Returns true if @wq has waiting processes
 *
 * Please refer to the comment for swait_active.
 */
static inline bool swq_has_sleeper(struct swait_queue_head *wq)
{
	/*
	 * We need to be sure we are in sync with the list_add()
	 * modifications to the wait queue (task_list).
	 *
	 * This memory barrier should be paired with one on the
	 * waiting side.
	 */
	smp_mb();
	return swait_active(wq);
}

extern void swake_up(struct swait_queue_head *q);
extern void swake_up_all(struct swait_queue_head *q);
extern void swake_up_locked(struct swait_queue_head *q);

extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state);
extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);

extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait);

/* as per ___wait_event() but for swait, therefore "exclusive == 0" */
#define ___swait_event(wq, condition, state, ret, cmd)			\
({									\
	struct swait_queue __wait;					\
	long __ret = ret;						\
									\
	INIT_LIST_HEAD(&__wait.task_list);				\
	for (;;) {							\
		long __int = prepare_to_swait_event(&wq, &__wait, state);\
									\
		if (condition)						\
			break;						\
									\
		if (___wait_is_interruptible(state) && __int) {		\
			__ret = __int;					\
			break;						\
		}							\
									\
		cmd;							\
	}								\
	finish_swait(&wq, &__wait);					\
	__ret;								\
})

#define __swait_event(wq, condition)					\
	(void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0,	\
			    schedule())

#define swait_event(wq, condition)					\
do {									\
	if (condition)							\
		break;							\
	__swait_event(wq, condition);					\
} while (0)

#define __swait_event_timeout(wq, condition, timeout)			\
	___swait_event(wq, ___wait_cond_timeout(condition),		\
		      TASK_UNINTERRUPTIBLE, timeout,			\
		      __ret = schedule_timeout(__ret))

#define swait_event_timeout(wq, condition, timeout)			\
({									\
	long __ret = timeout;						\
	if (!___wait_cond_timeout(condition))				\
		__ret = __swait_event_timeout(wq, condition, timeout);	\
	__ret;								\
})

#define __swait_event_interruptible(wq, condition)			\
	___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0,		\
		      schedule())

#define swait_event_interruptible(wq, condition)			\
({									\
	int __ret = 0;							\
	if (!(condition))						\
		__ret = __swait_event_interruptible(wq, condition);	\
	__ret;								\
})

#define __swait_event_interruptible_timeout(wq, condition, timeout)	\
	___swait_event(wq, ___wait_cond_timeout(condition),		\
		      TASK_INTERRUPTIBLE, timeout,			\
		      __ret = schedule_timeout(__ret))

#define swait_event_interruptible_timeout(wq, condition, timeout)	\
({									\
	long __ret = timeout;						\
	if (!___wait_cond_timeout(condition))				\
		__ret = __swait_event_interruptible_timeout(wq,		\
						condition, timeout);	\
	__ret;								\
})

#define __swait_event_idle(wq, condition)				\
	(void)___swait_event(wq, condition, TASK_IDLE, 0, schedule())

/**
 * swait_event_idle - wait without system load contribution
 * @wq: the waitqueue to wait on
 * @condition: a C expression for the event to wait for
 *
 * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
 * true. The @condition is checked each time the waitqueue @wq is woken up.
 *
 * This function is mostly used when a kthread or workqueue waits for some
 * condition and doesn't want to contribute to system load. Signals are
 * ignored.
 */
#define swait_event_idle(wq, condition)					\
do {									\
	if (condition)							\
		break;							\
	__swait_event_idle(wq, condition);				\
} while (0)

#define __swait_event_idle_timeout(wq, condition, timeout)		\
	___swait_event(wq, ___wait_cond_timeout(condition),		\
		       TASK_IDLE, timeout,				\
		       __ret = schedule_timeout(__ret))

/**
 * swait_event_idle_timeout - wait up to timeout without load contribution
 * @wq: the waitqueue to wait on
 * @condition: a C expression for the event to wait for
 * @timeout: timeout at which we'll give up in jiffies
 *
 * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
 * true. The @condition is checked each time the waitqueue @wq is woken up.
 *
 * This function is mostly used when a kthread or workqueue waits for some
 * condition and doesn't want to contribute to system load. Signals are
 * ignored.
 *
 * Returns:
 * 0 if the @condition evaluated to %false after the @timeout elapsed,
 * 1 if the @condition evaluated to %true after the @timeout elapsed,
 * or the remaining jiffies (at least 1) if the @condition evaluated
 * to %true before the @timeout elapsed.
 */
#define swait_event_idle_timeout(wq, condition, timeout)		\
({									\
	long __ret = timeout;						\
	if (!___wait_cond_timeout(condition))				\
		__ret = __swait_event_idle_timeout(wq,			\
						   condition, timeout);	\
	__ret;								\
})

#endif /* _LINUX_SWAIT_H */
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>
	8	#include <asm/current.h>
	9
	10	/*
	11	* Simple wait queues
	12	*
	13	* While these are very similar to the other/complex wait queues (wait.h) the
	14	* most important difference is that the simple waitqueue allows for
	15	* deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold
	16	* times.
	17	*
	18	* In order to make this so, we had to drop a fair number of features of the
	19	* other waitqueue code; notably:
	20	*
	21	* - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;
	22	* all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
	23	* sleeper state.
	24	*
	25	* - the exclusive mode; because this requires preserving the list order
	26	* and this is hard.
	27	*
	28	* - custom wake functions; because you cannot give any guarantees about
	29	* random code.
	30	*
	31	* As a side effect of this; the data structures are slimmer.
	32	*
	33	* One would recommend using this wait queue where possible.
	34	*/
	35
	36	struct task_struct;
	37
	38	struct swait_queue_head {
	39	raw_spinlock_t lock;
	40	struct list_head task_list;
	41	};
	42
	43	struct swait_queue {
	44	struct task_struct *task;
	45	struct list_head task_list;
	46	};
	47
	48	#define __SWAITQUEUE_INITIALIZER(name) { \
	49	.task = current, \
	50	.task_list = LIST_HEAD_INIT((name).task_list), \
	51	}
	52
	53	#define DECLARE_SWAITQUEUE(name) \
	54	struct swait_queue name = __SWAITQUEUE_INITIALIZER(name)
	55
	56	#define __SWAIT_QUEUE_HEAD_INITIALIZER(name) { \
	57	.lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \
	58	.task_list = LIST_HEAD_INIT((name).task_list), \
	59	}
	60
	61	#define DECLARE_SWAIT_QUEUE_HEAD(name) \
	62	struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name)
	63
	64	extern void __init_swait_queue_head(struct swait_queue_head q, const char name,
	65	struct lock_class_key *key);
66
67	#define init_swait_queue_head(q) \
68	do { \
69	static struct lock_class_key __key; \
70	__init_swait_queue_head((q), #q, &__key); \
71	} while (0)
72
73	#ifdef CONFIG_LOCKDEP
74	# define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) \
75	({ init_swait_queue_head(&name); name; })
76	# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \
77	struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)
78	#else
79	# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \
80	DECLARE_SWAIT_QUEUE_HEAD(name)
81	#endif
82
8cd641e3 DB	83	/**
	84	* swait_active -- locklessly test for waiters on the queue
	85	* @wq: the waitqueue to test for waiters
	86	*
	87	* returns true if the wait list is not empty
	88	*
	89	* NOTE: this function is lockless and requires care, incorrect usage _will_
	90	* lead to sporadic and non-obvious failure.
	91	*
	92	* NOTE2: this function has the same above implications as regular waitqueues.
	93	*
	94	* Use either while holding swait_queue_head::lock or when used for wakeups
	95	* with an extra smp_mb() like:
	96	*
	97	* CPU0 - waker CPU1 - waiter
	98	*
	99	* for (;;) {
	100	* @cond = true; prepare_to_swait(&wq_head, &wait, state);
	101	* smp_mb(); // smp_mb() from set_current_state()
	102	* if (swait_active(wq_head)) if (@cond)
	103	* wake_up(wq_head); break;
	104	* schedule();
	105	* }
	106	* finish_swait(&wq_head, &wait);
	107	*
	108	* Because without the explicit smp_mb() it's possible for the
	109	* swait_active() load to get hoisted over the @cond store such that we'll
	110	* observe an empty wait list while the waiter might not observe @cond.
	111	* This, in turn, can trigger missing wakeups.
	112	*
	113	* Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
	114	* which (when the lock is uncontended) are of roughly equal cost.
	115	*/
	116	static inline int swait_active(struct swait_queue_head *wq)
	117	{
	118	return !list_empty(&wq->task_list);
	119	}
	120
	121	/**
	122	* swq_has_sleeper - check if there are any waiting processes
	123	* @wq: the waitqueue to test for waiters
	124	*
	125	* Returns true if @wq has waiting processes
	126	*
	127	* Please refer to the comment for swait_active.
	128	*/
	129	static inline bool swq_has_sleeper(struct swait_queue_head *wq)
13b35686	130	{
8cd641e3 DB	131	/*
	132	* We need to be sure we are in sync with the list_add()
	133	* modifications to the wait queue (task_list).
	134	*
	135	* This memory barrier should be paired with one on the
	136	* waiting side.
	137	*/
	138	smp_mb();
	139	return swait_active(wq);
13b35686 PZI	140	}
	141
	142	extern void swake_up(struct swait_queue_head *q);
	143	extern void swake_up_all(struct swait_queue_head *q);
	144	extern void swake_up_locked(struct swait_queue_head *q);
	145
	146	extern void __prepare_to_swait(struct swait_queue_head q, struct swait_queue wait);
	147	extern void prepare_to_swait(struct swait_queue_head q, struct swait_queue wait, int state);
	148	extern long prepare_to_swait_event(struct swait_queue_head q, struct swait_queue wait, int state);
	149
	150	extern void __finish_swait(struct swait_queue_head q, struct swait_queue wait);
	151	extern void finish_swait(struct swait_queue_head q, struct swait_queue wait);
	152
	153	/* as per ___wait_event() but for swait, therefore "exclusive == 0" */
	154	#define ___swait_event(wq, condition, state, ret, cmd) \
	155	({ \
	156	struct swait_queue __wait; \
	157	long __ret = ret; \
	158	\
	159	INIT_LIST_HEAD(&__wait.task_list); \
	160	for (;;) { \
	161	long __int = prepare_to_swait_event(&wq, &__wait, state);\
	162	\
	163	if (condition) \
	164	break; \
	165	\
	166	if (___wait_is_interruptible(state) && __int) { \
	167	__ret = __int; \
	168	break; \
	169	} \
	170	\
	171	cmd; \
	172	} \
	173	finish_swait(&wq, &__wait); \
	174	__ret; \
	175	})
	176
	177	#define __swait_event(wq, condition) \
	178	(void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, \
	179	schedule())
	180
	181	#define swait_event(wq, condition) \
	182	do { \
	183	if (condition) \
	184	break; \
	185	__swait_event(wq, condition); \
	186	} while (0)
	187
	188	#define __swait_event_timeout(wq, condition, timeout) \
	189	___swait_event(wq, ___wait_cond_timeout(condition), \
	190	TASK_UNINTERRUPTIBLE, timeout, \
	191	__ret = schedule_timeout(__ret))
	192
	193	#define swait_event_timeout(wq, condition, timeout) \
	194	({ \
	195	long __ret = timeout; \
	196	if (!___wait_cond_timeout(condition)) \
	197	__ret = __swait_event_timeout(wq, condition, timeout); \
	198	__ret; \
	199	})
	200
	201	#define __swait_event_interruptible(wq, condition) \
	202	___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0, \
	203	schedule())
204
205	#define swait_event_interruptible(wq, condition) \
206	({ \
207	int __ret = 0; \
208	if (!(condition)) \
209	__ret = __swait_event_interruptible(wq, condition); \
210	__ret; \
211	})
212
213	#define __swait_event_interruptible_timeout(wq, condition, timeout) \
214	___swait_event(wq, ___wait_cond_timeout(condition), \
215	TASK_INTERRUPTIBLE, timeout, \
216	__ret = schedule_timeout(__ret))
217
218	#define swait_event_interruptible_timeout(wq, condition, timeout) \
219	({ \
220	long __ret = timeout; \
221	if (!___wait_cond_timeout(condition)) \
222	__ret = __swait_event_interruptible_timeout(wq, \
223	condition, timeout); \
224	__ret; \
225	})
226
352eee12 LR	227	#define __swait_event_idle(wq, condition) \
	228	(void)___swait_event(wq, condition, TASK_IDLE, 0, schedule())
	229
	230	/**
	231	* swait_event_idle - wait without system load contribution
	232	* @wq: the waitqueue to wait on
	233	* @condition: a C expression for the event to wait for
	234	*
	235	* The process is put to sleep (TASK_IDLE) until the @condition evaluates to
	236	* true. The @condition is checked each time the waitqueue @wq is woken up.
	237	*
	238	* This function is mostly used when a kthread or workqueue waits for some
	239	* condition and doesn't want to contribute to system load. Signals are
	240	* ignored.
	241	*/
	242	#define swait_event_idle(wq, condition) \
	243	do { \
	244	if (condition) \
	245	break; \
	246	__swait_event_idle(wq, condition); \
	247	} while (0)
	248
	249	#define __swait_event_idle_timeout(wq, condition, timeout) \
	250	___swait_event(wq, ___wait_cond_timeout(condition), \
	251	TASK_IDLE, timeout, \
	252	__ret = schedule_timeout(__ret))
	253
	254	/**
	255	* swait_event_idle_timeout - wait up to timeout without load contribution
	256	* @wq: the waitqueue to wait on
	257	* @condition: a C expression for the event to wait for
	258	* @timeout: timeout at which we'll give up in jiffies
	259	*
	260	* The process is put to sleep (TASK_IDLE) until the @condition evaluates to
	261	* true. The @condition is checked each time the waitqueue @wq is woken up.
	262	*
	263	* This function is mostly used when a kthread or workqueue waits for some
	264	* condition and doesn't want to contribute to system load. Signals are
	265	* ignored.
	266	*
	267	* Returns:
	268	* 0 if the @condition evaluated to %false after the @timeout elapsed,
	269	* 1 if the @condition evaluated to %true after the @timeout elapsed,
	270	* or the remaining jiffies (at least 1) if the @condition evaluated
	271	* to %true before the @timeout elapsed.
	272	*/
	273	#define swait_event_idle_timeout(wq, condition, timeout) \
	274	({ \
	275	long __ret = timeout; \
	276	if (!___wait_cond_timeout(condition)) \
	277	__ret = __swait_event_idle_timeout(wq, \
	278	condition, timeout); \
	279	__ret; \
	280	})
	281
13b35686	282	#endif /* _LINUX_SWAIT_H */