+++ /dev/null
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * Copyright (c) 2008 Intel Corporation
- * Author: Matthew Wilcox <willy@linux.intel.com>
- *
- * 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 <linux/compiler.h>
-#include <linux/kernel.h>
-#include <linux/export.h>
-#include <linux/sched.h>
-#include <linux/semaphore.h>
-#include <linux/spinlock.h>
-
-static noinline void __down(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_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 semaphore_waiter waiter;
-
- list_add_tail(&waiter.list, &sem->wait_list);
- waiter.task = current;
- waiter.up = false;
-
- for (;;) {
- if (unlikely(timeout <= 0))
- goto timed_out;
- __set_current_state(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 -ETIME;
-}
-
-static noinline void __sched __down(struct semaphore *sem)
-{
- __down_common(sem, TASK_UNINTERRUPTIBLE, 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);
-}
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