| /* 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 <linux/wait.h> |
| #include <asm/current.h> |
| |
| /* |
| * Simple waitqueues are semantically very different to regular 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. |
| * |
| * Mainly, this is accomplished by two things. Firstly not allowing swake_up_all |
| * from IRQ disabled, and dropping the lock upon every wakeup, giving a higher |
| * priority task a chance to run. |
| * |
| * Secondly, 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 that leads to O(n) wakeups, everything is |
| * exclusive. As such swake_up_one will only ever awake _one_ waiter. |
| * |
| * - custom wake callback functions; because you cannot give any guarantees |
| * about random code. This also allows swait to be used in RT, such that |
| * raw spinlock can be used for the swait queue head. |
| * |
| * As a side effect of these; the data structures are slimmer albeit more ad-hoc. |
| * For all the above, note that simple wait queues should _only_ be used under |
| * very specific realtime constraints -- it is best to stick with the regular |
| * wait queues in most cases. |
| */ |
| |
| 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_exclusive(&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_one(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_exclusive(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 == 1" */ |
| #define ___swait_event(wq, condition, state, ret, cmd) \ |
| ({ \ |
| __label__ __out; \ |
| 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; \ |
| goto __out; \ |
| } \ |
| \ |
| cmd; \ |
| } \ |
| finish_swait(&wq, &__wait); \ |
| __out: __ret; \ |
| }) |
| |
| #define __swait_event(wq, condition) \ |
| (void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, \ |
| schedule()) |
| |
| #define swait_event_exclusive(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_exclusive(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_exclusive(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_exclusive(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_exclusive - 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_exclusive(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_exclusive - 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_exclusive(wq, condition, timeout) \ |
| ({ \ |
| long __ret = timeout; \ |
| if (!___wait_cond_timeout(condition)) \ |
| __ret = __swait_event_idle_timeout(wq, \ |
| condition, timeout); \ |
| __ret; \ |
| }) |
| |
| #endif /* _LINUX_SWAIT_H */ |