wait-simple: Simple waitqueue implementation
wait_queue is a swiss army knife and in most of the cases the complexity is not needed. For RT waitqueues are a constant source of trouble as we can't convert the head lock to a raw spinlock due to fancy and long lasting callbacks. Provide a slim version, which allows RT to replace wait queues. This should go mainline as well, as it lowers memory consumption and runtime overhead. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> smp_mb() added by Steven Rostedt to fix a race condition with swait wakeups vs adding items to the list.
This commit is contained in:
Thomas Gleixner
parent
e49d664aa7
commit
99076b3731
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#ifndef _LINUX_WAIT_SIMPLE_H
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#define _LINUX_WAIT_SIMPLE_H
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#include <linux/spinlock.h>
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#include <linux/list.h>
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#include <asm/current.h>
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struct swaiter {
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struct task_struct *task;
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struct list_head node;
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};
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#define DEFINE_SWAITER(name) \
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struct swaiter name = { \
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.task = current, \
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.node = LIST_HEAD_INIT((name).node), \
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}
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struct swait_head {
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raw_spinlock_t lock;
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struct list_head list;
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};
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#define DEFINE_SWAIT_HEAD(name) \
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struct swait_head name = { \
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.lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \
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.list = LIST_HEAD_INIT((name).list), \
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}
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extern void __init_swait_head(struct swait_head *h, struct lock_class_key *key);
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#define init_swait_head(swh) \
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do { \
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static struct lock_class_key __key; \
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\
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__init_swait_head((swh), &__key); \
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} while (0)
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/*
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* Waiter functions
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*/
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static inline bool swaiter_enqueued(struct swaiter *w)
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{
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return w->task != NULL;
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}
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extern void swait_prepare(struct swait_head *head, struct swaiter *w, int state);
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extern void swait_finish(struct swait_head *head, struct swaiter *w);
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/*
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* Adds w to head->list. Must be called with head->lock locked.
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*/
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static inline void __swait_enqueue(struct swait_head *head, struct swaiter *w)
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{
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list_add(&w->node, &head->list);
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/* We can't let the condition leak before the setting of head */
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smp_mb();
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}
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/*
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* Removes w from head->list. Must be called with head->lock locked.
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*/
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static inline void __swait_dequeue(struct swaiter *w)
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{
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list_del_init(&w->node);
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}
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/*
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* Check whether a head has waiters enqueued
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*/
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static inline bool swait_head_has_waiters(struct swait_head *h)
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{
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/* Make sure the condition is visible before checking list_empty() */
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smp_mb();
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return !list_empty(&h->list);
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}
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/*
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* Wakeup functions
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*/
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extern int __swait_wake(struct swait_head *head, unsigned int state);
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static inline int swait_wake(struct swait_head *head)
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{
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return swait_head_has_waiters(head) ?
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__swait_wake(head, TASK_NORMAL) : 0;
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}
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static inline int swait_wake_interruptible(struct swait_head *head)
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{
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return swait_head_has_waiters(head) ?
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__swait_wake(head, TASK_INTERRUPTIBLE) : 0;
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}
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/*
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* Event API
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*/
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#define __swait_event(wq, condition) \
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do { \
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DEFINE_SWAITER(__wait); \
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\
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for (;;) { \
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swait_prepare(&wq, &__wait, TASK_UNINTERRUPTIBLE); \
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if (condition) \
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break; \
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schedule(); \
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} \
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swait_finish(&wq, &__wait); \
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} while (0)
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/**
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* swait_event - sleep until a condition gets true
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* @wq: the waitqueue to wait on
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* @condition: a C expression for the event to wait for
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*
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* The process is put to sleep (TASK_UNINTERRUPTIBLE) until the
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* @condition evaluates to true. The @condition is checked each time
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* the waitqueue @wq is woken up.
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*
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* wake_up() has to be called after changing any variable that could
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* change the result of the wait condition.
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*/
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#define swait_event(wq, condition) \
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do { \
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if (condition) \
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break; \
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__swait_event(wq, condition); \
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} while (0)
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#define __swait_event_interruptible(wq, condition, ret) \
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do { \
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DEFINE_SWAITER(__wait); \
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\
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for (;;) { \
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swait_prepare(&wq, &__wait, TASK_INTERRUPTIBLE); \
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if (condition) \
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break; \
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if (signal_pending(current)) { \
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ret = -ERESTARTSYS; \
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break; \
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} \
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schedule(); \
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} \
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swait_finish(&wq, &__wait); \
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} while (0)
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#define __swait_event_interruptible_timeout(wq, condition, ret) \
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do { \
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DEFINE_SWAITER(__wait); \
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\
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for (;;) { \
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swait_prepare(&wq, &__wait, TASK_INTERRUPTIBLE); \
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if (condition) \
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break; \
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if (signal_pending(current)) { \
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ret = -ERESTARTSYS; \
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break; \
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} \
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ret = schedule_timeout(ret); \
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if (!ret) \
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break; \
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} \
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swait_finish(&wq, &__wait); \
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} while (0)
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/**
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* swait_event_interruptible - sleep until a condition gets true
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* @wq: the waitqueue to wait on
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* @condition: a C expression for the event to wait for
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*
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* The process is put to sleep (TASK_INTERRUPTIBLE) until the
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* @condition evaluates to true. The @condition is checked each time
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* the waitqueue @wq is woken up.
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*
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* wake_up() has to be called after changing any variable that could
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* change the result of the wait condition.
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*/
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#define swait_event_interruptible(wq, condition) \
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({ \
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int __ret = 0; \
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if (!(condition)) \
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__swait_event_interruptible(wq, condition, __ret); \
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__ret; \
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})
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#define swait_event_interruptible_timeout(wq, condition, timeout) \
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({ \
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int __ret = timeout; \
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if (!(condition)) \
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__swait_event_interruptible_timeout(wq, condition, __ret); \
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__ret; \
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})
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#define __swait_event_timeout(wq, condition, ret) \
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do { \
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DEFINE_SWAITER(__wait); \
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\
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for (;;) { \
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swait_prepare(&wq, &__wait, TASK_UNINTERRUPTIBLE); \
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if (condition) \
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break; \
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ret = schedule_timeout(ret); \
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if (!ret) \
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break; \
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} \
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swait_finish(&wq, &__wait); \
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} while (0)
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/**
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* swait_event_timeout - sleep until a condition gets true or a timeout elapses
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* @wq: the waitqueue to wait on
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* @condition: a C expression for the event to wait for
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* @timeout: timeout, in jiffies
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*
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* The process is put to sleep (TASK_UNINTERRUPTIBLE) until the
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* @condition evaluates to true. The @condition is checked each time
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* the waitqueue @wq is woken up.
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*
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* wake_up() has to be called after changing any variable that could
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* change the result of the wait condition.
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*
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* The function returns 0 if the @timeout elapsed, and the remaining
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* jiffies if the condition evaluated to true before the timeout elapsed.
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*/
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#define swait_event_timeout(wq, condition, timeout) \
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({ \
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long __ret = timeout; \
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if (!(condition)) \
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__swait_event_timeout(wq, condition, __ret); \
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__ret; \
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})
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#endif
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@ -13,7 +13,7 @@ endif
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obj-y += core.o proc.o clock.o cputime.o
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obj-y += idle_task.o fair.o rt.o deadline.o stop_task.o
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obj-y += wait.o completion.o
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obj-y += wait.o wait-simple.o completion.o
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obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o
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obj-$(CONFIG_SCHED_AUTOGROUP) += auto_group.o
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obj-$(CONFIG_SCHEDSTATS) += stats.o
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@ -0,0 +1,68 @@
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/*
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* Simple waitqueues without fancy flags and callbacks
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*
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* (C) 2011 Thomas Gleixner <tglx@linutronix.de>
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*
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* Based on kernel/wait.c
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*
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* For licencing details see kernel-base/COPYING
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*/
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#include <linux/init.h>
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#include <linux/export.h>
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#include <linux/sched.h>
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#include <linux/wait-simple.h>
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void __init_swait_head(struct swait_head *head, struct lock_class_key *key)
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{
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raw_spin_lock_init(&head->lock);
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lockdep_set_class(&head->lock, key);
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INIT_LIST_HEAD(&head->list);
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}
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EXPORT_SYMBOL(__init_swait_head);
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void swait_prepare(struct swait_head *head, struct swaiter *w, int state)
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{
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unsigned long flags;
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raw_spin_lock_irqsave(&head->lock, flags);
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w->task = current;
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if (list_empty(&w->node))
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__swait_enqueue(head, w);
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set_current_state(state);
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raw_spin_unlock_irqrestore(&head->lock, flags);
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}
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EXPORT_SYMBOL(swait_prepare);
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void swait_finish(struct swait_head *head, struct swaiter *w)
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{
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unsigned long flags;
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__set_current_state(TASK_RUNNING);
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if (w->task) {
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raw_spin_lock_irqsave(&head->lock, flags);
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__swait_dequeue(w);
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raw_spin_unlock_irqrestore(&head->lock, flags);
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}
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}
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EXPORT_SYMBOL(swait_finish);
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int __swait_wake(struct swait_head *head, unsigned int state)
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{
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struct swaiter *curr, *next;
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unsigned long flags;
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int woken = 0;
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raw_spin_lock_irqsave(&head->lock, flags);
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list_for_each_entry_safe(curr, next, &head->list, node) {
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if (wake_up_state(curr->task, state)) {
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__swait_dequeue(curr);
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curr->task = NULL;
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woken++;
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}
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}
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raw_spin_unlock_irqrestore(&head->lock, flags);
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return woken;
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}
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EXPORT_SYMBOL(__swait_wake);
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