301 строка
10 KiB
C
301 строка
10 KiB
C
/* 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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* BROKEN wait-queues.
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*
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* These "simple" wait-queues are broken garbage, and should never be
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* used. The comments below claim that they are "similar" to regular
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* wait-queues, but the semantics are actually completely different, and
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* every single user we have ever had has been buggy (or pointless).
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*
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* A "swake_up_one()" only wakes up _one_ waiter, which is not at all what
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* "wake_up()" does, and has led to problems. In other cases, it has
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* been fine, because there's only ever one waiter (kvm), but in that
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* case gthe whole "simple" wait-queue is just pointless to begin with,
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* since there is no "queue". Use "wake_up_process()" with a direct
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* pointer instead.
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*
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* While these are very similar to regular wait queues (wait.h) the most
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* important difference is that the simple waitqueue allows for deterministic
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* behaviour -- IOW it has strictly bounded IRQ and lock hold 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.
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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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