From b33fc8298f7e13226b9895abc57c9bfce5e3fa2d Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Sun, 8 Jan 2017 00:13:18 -0900 Subject: bcache in userspace; userspace fsck --- linux/semaphore.c | 256 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 256 insertions(+) create mode 100644 linux/semaphore.c (limited to 'linux/semaphore.c') diff --git a/linux/semaphore.c b/linux/semaphore.c new file mode 100644 index 00000000..6561dd22 --- /dev/null +++ b/linux/semaphore.c @@ -0,0 +1,256 @@ +/* + * Copyright (c) 2008 Intel Corporation + * Author: Matthew Wilcox + * + * Distributed under the terms of the GNU GPL, version 2 + * + * This file implements counting semaphores. + * A counting semaphore may be acquired 'n' times before sleeping. + * See mutex.c for single-acquisition sleeping locks which enforce + * rules which allow code to be debugged more easily. + */ + +/* + * Some notes on the implementation: + * + * The spinlock controls access to the other members of the semaphore. + * down_trylock() and up() can be called from interrupt context, so we + * have to disable interrupts when taking the lock. It turns out various + * parts of the kernel expect to be able to use down() on a semaphore in + * interrupt context when they know it will succeed, so we have to use + * irqsave variants for down(), down_interruptible() and down_killable() + * too. + * + * The ->count variable represents how many more tasks can acquire this + * semaphore. If it's zero, there may be tasks waiting on the wait_list. + */ + +#include +#include +#include +#include +#include +#include + +static noinline void __down(struct semaphore *sem); +static noinline int __down_interruptible(struct semaphore *sem); +static noinline int __down_killable(struct semaphore *sem); +static noinline int __down_timeout(struct semaphore *sem, long timeout); +static noinline void __up(struct semaphore *sem); + +/** + * down - acquire the semaphore + * @sem: the semaphore to be acquired + * + * Acquires the semaphore. If no more tasks are allowed to acquire the + * semaphore, calling this function will put the task to sleep until the + * semaphore is released. + * + * Use of this function is deprecated, please use down_interruptible() or + * down_killable() instead. + */ +void down(struct semaphore *sem) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&sem->lock, flags); + if (likely(sem->count > 0)) + sem->count--; + else + __down(sem); + raw_spin_unlock_irqrestore(&sem->lock, flags); +} +EXPORT_SYMBOL(down); + +/** + * down_interruptible - acquire the semaphore unless interrupted + * @sem: the semaphore to be acquired + * + * Attempts to acquire the semaphore. If no more tasks are allowed to + * acquire the semaphore, calling this function will put the task to sleep. + * If the sleep is interrupted by a signal, this function will return -EINTR. + * If the semaphore is successfully acquired, this function returns 0. + */ +int down_interruptible(struct semaphore *sem) +{ + unsigned long flags; + int result = 0; + + raw_spin_lock_irqsave(&sem->lock, flags); + if (likely(sem->count > 0)) + sem->count--; + else + result = __down_interruptible(sem); + raw_spin_unlock_irqrestore(&sem->lock, flags); + + return result; +} +EXPORT_SYMBOL(down_interruptible); + +/** + * down_killable - acquire the semaphore unless killed + * @sem: the semaphore to be acquired + * + * Attempts to acquire the semaphore. If no more tasks are allowed to + * acquire the semaphore, calling this function will put the task to sleep. + * If the sleep is interrupted by a fatal signal, this function will return + * -EINTR. If the semaphore is successfully acquired, this function returns + * 0. + */ +int down_killable(struct semaphore *sem) +{ + unsigned long flags; + int result = 0; + + raw_spin_lock_irqsave(&sem->lock, flags); + if (likely(sem->count > 0)) + sem->count--; + else + result = __down_killable(sem); + raw_spin_unlock_irqrestore(&sem->lock, flags); + + return result; +} +EXPORT_SYMBOL(down_killable); + +/** + * down_trylock - try to acquire the semaphore, without waiting + * @sem: the semaphore to be acquired + * + * Try to acquire the semaphore atomically. Returns 0 if the semaphore has + * been acquired successfully or 1 if it it cannot be acquired. + * + * NOTE: This return value is inverted from both spin_trylock and + * mutex_trylock! Be careful about this when converting code. + * + * Unlike mutex_trylock, this function can be used from interrupt context, + * and the semaphore can be released by any task or interrupt. + */ +int down_trylock(struct semaphore *sem) +{ + unsigned long flags; + int count; + + raw_spin_lock_irqsave(&sem->lock, flags); + count = sem->count - 1; + if (likely(count >= 0)) + sem->count = count; + raw_spin_unlock_irqrestore(&sem->lock, flags); + + return (count < 0); +} +EXPORT_SYMBOL(down_trylock); + +/** + * down_timeout - acquire the semaphore within a specified time + * @sem: the semaphore to be acquired + * @timeout: how long to wait before failing + * + * Attempts to acquire the semaphore. If no more tasks are allowed to + * acquire the semaphore, calling this function will put the task to sleep. + * If the semaphore is not released within the specified number of jiffies, + * this function returns -ETIME. It returns 0 if the semaphore was acquired. + */ +int down_timeout(struct semaphore *sem, long timeout) +{ + unsigned long flags; + int result = 0; + + raw_spin_lock_irqsave(&sem->lock, flags); + if (likely(sem->count > 0)) + sem->count--; + else + result = __down_timeout(sem, timeout); + raw_spin_unlock_irqrestore(&sem->lock, flags); + + return result; +} +EXPORT_SYMBOL(down_timeout); + +/** + * up - release the semaphore + * @sem: the semaphore to release + * + * Release the semaphore. Unlike mutexes, up() may be called from any + * context and even by tasks which have never called down(). + */ +void up(struct semaphore *sem) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&sem->lock, flags); + if (likely(list_empty(&sem->wait_list))) + sem->count++; + else + __up(sem); + raw_spin_unlock_irqrestore(&sem->lock, flags); +} +EXPORT_SYMBOL(up); + +/* Functions for the contended case */ + +struct semaphore_waiter { + struct list_head list; + struct task_struct *task; + bool up; +}; + +/* + * Because this function is inlined, the 'state' parameter will be + * constant, and thus optimised away by the compiler. Likewise the + * 'timeout' parameter for the cases without timeouts. + */ +static inline int __sched __down_common(struct semaphore *sem, long state, + long timeout) +{ + struct task_struct *task = current; + struct semaphore_waiter waiter; + + list_add_tail(&waiter.list, &sem->wait_list); + waiter.task = task; + waiter.up = false; + + for (;;) { + if (unlikely(timeout <= 0)) + goto timed_out; + __set_task_state(task, state); + raw_spin_unlock_irq(&sem->lock); + timeout = schedule_timeout(timeout); + raw_spin_lock_irq(&sem->lock); + if (waiter.up) + return 0; + } + + timed_out: + list_del(&waiter.list); + return -1; +} + +static noinline void __sched __down(struct semaphore *sem) +{ + __down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); +} + +static noinline int __sched __down_interruptible(struct semaphore *sem) +{ + return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); +} + +static noinline int __sched __down_killable(struct semaphore *sem) +{ + return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT); +} + +static noinline int __sched __down_timeout(struct semaphore *sem, long timeout) +{ + return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout); +} + +static noinline void __sched __up(struct semaphore *sem) +{ + struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list, + struct semaphore_waiter, list); + list_del(&waiter->list); + waiter->up = true; + wake_up_process(waiter->task); +} -- cgit v1.2.3