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287 lines
9.5 KiB
287 lines
9.5 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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#ifndef _LINUX_SWAIT_H |
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#define _LINUX_SWAIT_H |
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#include <linux/list.h> |
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#include <linux/stddef.h> |
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#include <linux/spinlock.h> |
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#include <linux/wait.h> |
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#include <asm/current.h> |
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/* |
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* Simple waitqueues are semantically very different to regular wait queues |
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* (wait.h). The most important difference is that the simple waitqueue allows |
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* for deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold |
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* times. |
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* |
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* Mainly, this is accomplished by two things. Firstly not allowing swake_up_all |
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* from IRQ disabled, and dropping the lock upon every wakeup, giving a higher |
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* priority task a chance to run. |
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* |
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* Secondly, we had to drop a fair number of features of the other waitqueue |
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* code; notably: |
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* |
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* - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue; |
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* all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right |
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* sleeper state. |
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* |
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* - the !exclusive mode; because that leads to O(n) wakeups, everything is |
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* exclusive. As such swake_up_one will only ever awake _one_ waiter. |
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* |
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* - custom wake callback functions; because you cannot give any guarantees |
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* about random code. This also allows swait to be used in RT, such that |
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* raw spinlock can be used for the swait queue head. |
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* |
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* As a side effect of these; the data structures are slimmer albeit more ad-hoc. |
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* For all the above, note that simple wait queues should _only_ be used under |
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* very specific realtime constraints -- it is best to stick with the regular |
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* wait queues in most cases. |
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*/ |
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struct task_struct; |
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struct swait_queue_head { |
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raw_spinlock_t lock; |
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struct list_head task_list; |
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}; |
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struct swait_queue { |
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struct task_struct *task; |
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struct list_head task_list; |
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}; |
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#define __SWAITQUEUE_INITIALIZER(name) { \ |
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.task = current, \ |
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.task_list = LIST_HEAD_INIT((name).task_list), \ |
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} |
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#define DECLARE_SWAITQUEUE(name) \ |
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struct swait_queue name = __SWAITQUEUE_INITIALIZER(name) |
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#define __SWAIT_QUEUE_HEAD_INITIALIZER(name) { \ |
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.lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \ |
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.task_list = LIST_HEAD_INIT((name).task_list), \ |
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} |
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#define DECLARE_SWAIT_QUEUE_HEAD(name) \ |
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struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name) |
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extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name, |
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struct lock_class_key *key); |
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#define init_swait_queue_head(q) \ |
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do { \ |
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static struct lock_class_key __key; \ |
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__init_swait_queue_head((q), #q, &__key); \ |
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} while (0) |
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#ifdef CONFIG_LOCKDEP |
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# define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) \ |
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({ init_swait_queue_head(&name); name; }) |
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# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \ |
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struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) |
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#else |
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# define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \ |
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DECLARE_SWAIT_QUEUE_HEAD(name) |
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#endif |
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/** |
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* swait_active -- locklessly test for waiters on the queue |
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* @wq: the waitqueue to test for waiters |
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* |
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* returns true if the wait list is not empty |
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* |
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* NOTE: this function is lockless and requires care, incorrect usage _will_ |
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* lead to sporadic and non-obvious failure. |
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* |
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* NOTE2: this function has the same above implications as regular waitqueues. |
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* |
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* Use either while holding swait_queue_head::lock or when used for wakeups |
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* with an extra smp_mb() like: |
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* |
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* CPU0 - waker CPU1 - waiter |
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* |
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* for (;;) { |
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* @cond = true; prepare_to_swait_exclusive(&wq_head, &wait, state); |
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* smp_mb(); // smp_mb() from set_current_state() |
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* if (swait_active(wq_head)) if (@cond) |
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* wake_up(wq_head); break; |
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* schedule(); |
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* } |
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* finish_swait(&wq_head, &wait); |
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* |
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* Because without the explicit smp_mb() it's possible for the |
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* swait_active() load to get hoisted over the @cond store such that we'll |
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* observe an empty wait list while the waiter might not observe @cond. |
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* This, in turn, can trigger missing wakeups. |
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* |
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* Also note that this 'optimization' trades a spin_lock() for an smp_mb(), |
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* which (when the lock is uncontended) are of roughly equal cost. |
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*/ |
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static inline int swait_active(struct swait_queue_head *wq) |
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{ |
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return !list_empty(&wq->task_list); |
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} |
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/** |
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* swq_has_sleeper - check if there are any waiting processes |
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* @wq: the waitqueue to test for waiters |
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* |
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* Returns true if @wq has waiting processes |
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* |
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* Please refer to the comment for swait_active. |
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*/ |
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static inline bool swq_has_sleeper(struct swait_queue_head *wq) |
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{ |
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/* |
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* We need to be sure we are in sync with the list_add() |
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* modifications to the wait queue (task_list). |
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* |
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* This memory barrier should be paired with one on the |
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* waiting side. |
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*/ |
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smp_mb(); |
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return swait_active(wq); |
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} |
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extern void swake_up_one(struct swait_queue_head *q); |
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extern void swake_up_all(struct swait_queue_head *q); |
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extern void swake_up_locked(struct swait_queue_head *q); |
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extern void prepare_to_swait_exclusive(struct swait_queue_head *q, struct swait_queue *wait, int state); |
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extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state); |
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extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait); |
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extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait); |
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/* as per ___wait_event() but for swait, therefore "exclusive == 1" */ |
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#define ___swait_event(wq, condition, state, ret, cmd) \ |
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({ \ |
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__label__ __out; \ |
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struct swait_queue __wait; \ |
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long __ret = ret; \ |
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\ |
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INIT_LIST_HEAD(&__wait.task_list); \ |
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for (;;) { \ |
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long __int = prepare_to_swait_event(&wq, &__wait, state);\ |
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\ |
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if (condition) \ |
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break; \ |
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\ |
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if (___wait_is_interruptible(state) && __int) { \ |
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__ret = __int; \ |
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goto __out; \ |
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} \ |
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\ |
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cmd; \ |
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} \ |
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finish_swait(&wq, &__wait); \ |
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__out: __ret; \ |
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}) |
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#define __swait_event(wq, condition) \ |
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(void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, \ |
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schedule()) |
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#define swait_event_exclusive(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_timeout(wq, condition, timeout) \ |
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___swait_event(wq, ___wait_cond_timeout(condition), \ |
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TASK_UNINTERRUPTIBLE, timeout, \ |
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__ret = schedule_timeout(__ret)) |
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#define swait_event_timeout_exclusive(wq, condition, timeout) \ |
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({ \ |
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long __ret = timeout; \ |
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if (!___wait_cond_timeout(condition)) \ |
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__ret = __swait_event_timeout(wq, condition, timeout); \ |
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__ret; \ |
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}) |
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#define __swait_event_interruptible(wq, condition) \ |
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___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0, \ |
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schedule()) |
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#define swait_event_interruptible_exclusive(wq, condition) \ |
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({ \ |
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int __ret = 0; \ |
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if (!(condition)) \ |
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__ret = __swait_event_interruptible(wq, condition); \ |
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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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___swait_event(wq, ___wait_cond_timeout(condition), \ |
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TASK_INTERRUPTIBLE, timeout, \ |
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__ret = schedule_timeout(__ret)) |
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#define swait_event_interruptible_timeout_exclusive(wq, condition, timeout)\ |
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({ \ |
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long __ret = timeout; \ |
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if (!___wait_cond_timeout(condition)) \ |
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__ret = __swait_event_interruptible_timeout(wq, \ |
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condition, timeout); \ |
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__ret; \ |
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}) |
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#define __swait_event_idle(wq, condition) \ |
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(void)___swait_event(wq, condition, TASK_IDLE, 0, schedule()) |
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/** |
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* swait_event_idle_exclusive - wait without system load contribution |
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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_IDLE) until the @condition evaluates to |
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* true. The @condition is checked each time the waitqueue @wq is woken up. |
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* |
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* This function is mostly used when a kthread or workqueue waits for some |
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* condition and doesn't want to contribute to system load. Signals are |
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* ignored. |
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*/ |
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#define swait_event_idle_exclusive(wq, condition) \ |
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do { \ |
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if (condition) \ |
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break; \ |
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__swait_event_idle(wq, condition); \ |
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} while (0) |
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#define __swait_event_idle_timeout(wq, condition, timeout) \ |
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___swait_event(wq, ___wait_cond_timeout(condition), \ |
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TASK_IDLE, timeout, \ |
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__ret = schedule_timeout(__ret)) |
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/** |
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* swait_event_idle_timeout_exclusive - wait up to timeout without load contribution |
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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 at which we'll give up in jiffies |
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* |
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* The process is put to sleep (TASK_IDLE) until the @condition evaluates to |
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* true. The @condition is checked each time the waitqueue @wq is woken up. |
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* |
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* This function is mostly used when a kthread or workqueue waits for some |
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* condition and doesn't want to contribute to system load. Signals are |
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* ignored. |
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* |
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* Returns: |
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* 0 if the @condition evaluated to %false after the @timeout elapsed, |
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* 1 if the @condition evaluated to %true after the @timeout elapsed, |
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* or the remaining jiffies (at least 1) if the @condition evaluated |
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* to %true before the @timeout elapsed. |
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*/ |
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#define swait_event_idle_timeout_exclusive(wq, condition, timeout) \ |
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({ \ |
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long __ret = timeout; \ |
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if (!___wait_cond_timeout(condition)) \ |
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__ret = __swait_event_idle_timeout(wq, \ |
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condition, timeout); \ |
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__ret; \ |
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}) |
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#endif /* _LINUX_SWAIT_H */
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