1/*
  2 * Copyright (c) 2008 Intel Corporation
  3 * Author: Matthew Wilcox <willy@linux.intel.com>
  4 *
  5 * Distributed under the terms of the GNU GPL, version 2
  6 *
  7 * This file implements counting semaphores.
  8 * A counting semaphore may be acquired 'n' times before sleeping.
  9 * See mutex.c for single-acquisition sleeping locks which enforce
 10 * rules which allow code to be debugged more easily.
 11 */
 12
 13/*
 14 * Some notes on the implementation:
 15 *
 16 * The spinlock controls access to the other members of the semaphore.
 17 * down_trylock() and up() can be called from interrupt context, so we
 18 * have to disable interrupts when taking the lock.  It turns out various
 19 * parts of the kernel expect to be able to use down() on a semaphore in
 20 * interrupt context when they know it will succeed, so we have to use
 21 * irqsave variants for down(), down_interruptible() and down_killable()
 22 * too.
 23 *
 24 * The ->count variable represents how many more tasks can acquire this
 25 * semaphore.  If it's zero, there may be tasks waiting on the wait_list.
 26 */
 27
 28#include <linux/compiler.h>
 29#include <linux/kernel.h>
 30#include <linux/export.h>
 31#include <linux/sched.h>
 32#include <linux/sched/debug.h>
 33#include <linux/semaphore.h>
 34#include <linux/spinlock.h>
 35#include <linux/ftrace.h>
 
 36
 37static noinline void __down(struct semaphore *sem);
 38static noinline int __down_interruptible(struct semaphore *sem);
 39static noinline int __down_killable(struct semaphore *sem);
 40static noinline int __down_timeout(struct semaphore *sem, long timeout);
 41static noinline void __up(struct semaphore *sem);
 42
 43/**
 44 * down - acquire the semaphore
 45 * @sem: the semaphore to be acquired
 46 *
 47 * Acquires the semaphore.  If no more tasks are allowed to acquire the
 48 * semaphore, calling this function will put the task to sleep until the
 49 * semaphore is released.
 50 *
 51 * Use of this function is deprecated, please use down_interruptible() or
 52 * down_killable() instead.
 53 */
 54void down(struct semaphore *sem)
 55{
 56	unsigned long flags;
 57
 
 58	raw_spin_lock_irqsave(&sem->lock, flags);
 59	if (likely(sem->count > 0))
 60		sem->count--;
 61	else
 62		__down(sem);
 63	raw_spin_unlock_irqrestore(&sem->lock, flags);
 64}
 65EXPORT_SYMBOL(down);
 66
 67/**
 68 * down_interruptible - acquire the semaphore unless interrupted
 69 * @sem: the semaphore to be acquired
 70 *
 71 * Attempts to acquire the semaphore.  If no more tasks are allowed to
 72 * acquire the semaphore, calling this function will put the task to sleep.
 73 * If the sleep is interrupted by a signal, this function will return -EINTR.
 74 * If the semaphore is successfully acquired, this function returns 0.
 75 */
 76int down_interruptible(struct semaphore *sem)
 77{
 78	unsigned long flags;
 79	int result = 0;
 80
 
 81	raw_spin_lock_irqsave(&sem->lock, flags);
 82	if (likely(sem->count > 0))
 83		sem->count--;
 84	else
 85		result = __down_interruptible(sem);
 86	raw_spin_unlock_irqrestore(&sem->lock, flags);
 87
 88	return result;
 89}
 90EXPORT_SYMBOL(down_interruptible);
 91
 92/**
 93 * down_killable - acquire the semaphore unless killed
 94 * @sem: the semaphore to be acquired
 95 *
 96 * Attempts to acquire the semaphore.  If no more tasks are allowed to
 97 * acquire the semaphore, calling this function will put the task to sleep.
 98 * If the sleep is interrupted by a fatal signal, this function will return
 99 * -EINTR.  If the semaphore is successfully acquired, this function returns
100 * 0.
101 */
102int down_killable(struct semaphore *sem)
103{
104	unsigned long flags;
105	int result = 0;
106
 
107	raw_spin_lock_irqsave(&sem->lock, flags);
108	if (likely(sem->count > 0))
109		sem->count--;
110	else
111		result = __down_killable(sem);
112	raw_spin_unlock_irqrestore(&sem->lock, flags);
113
114	return result;
115}
116EXPORT_SYMBOL(down_killable);
117
118/**
119 * down_trylock - try to acquire the semaphore, without waiting
120 * @sem: the semaphore to be acquired
121 *
122 * Try to acquire the semaphore atomically.  Returns 0 if the semaphore has
123 * been acquired successfully or 1 if it it cannot be acquired.
124 *
125 * NOTE: This return value is inverted from both spin_trylock and
126 * mutex_trylock!  Be careful about this when converting code.
127 *
128 * Unlike mutex_trylock, this function can be used from interrupt context,
129 * and the semaphore can be released by any task or interrupt.
130 */
131int down_trylock(struct semaphore *sem)
132{
133	unsigned long flags;
134	int count;
135
136	raw_spin_lock_irqsave(&sem->lock, flags);
137	count = sem->count - 1;
138	if (likely(count >= 0))
139		sem->count = count;
140	raw_spin_unlock_irqrestore(&sem->lock, flags);
141
142	return (count < 0);
143}
144EXPORT_SYMBOL(down_trylock);
145
146/**
147 * down_timeout - acquire the semaphore within a specified time
148 * @sem: the semaphore to be acquired
149 * @timeout: how long to wait before failing
150 *
151 * Attempts to acquire the semaphore.  If no more tasks are allowed to
152 * acquire the semaphore, calling this function will put the task to sleep.
153 * If the semaphore is not released within the specified number of jiffies,
154 * this function returns -ETIME.  It returns 0 if the semaphore was acquired.
155 */
156int down_timeout(struct semaphore *sem, long timeout)
157{
158	unsigned long flags;
159	int result = 0;
160
 
161	raw_spin_lock_irqsave(&sem->lock, flags);
162	if (likely(sem->count > 0))
163		sem->count--;
164	else
165		result = __down_timeout(sem, timeout);
166	raw_spin_unlock_irqrestore(&sem->lock, flags);
167
168	return result;
169}
170EXPORT_SYMBOL(down_timeout);
171
172/**
173 * up - release the semaphore
174 * @sem: the semaphore to release
175 *
176 * Release the semaphore.  Unlike mutexes, up() may be called from any
177 * context and even by tasks which have never called down().
178 */
179void up(struct semaphore *sem)
180{
181	unsigned long flags;
182
183	raw_spin_lock_irqsave(&sem->lock, flags);
184	if (likely(list_empty(&sem->wait_list)))
185		sem->count++;
186	else
187		__up(sem);
188	raw_spin_unlock_irqrestore(&sem->lock, flags);
189}
190EXPORT_SYMBOL(up);
191
192/* Functions for the contended case */
193
194struct semaphore_waiter {
195	struct list_head list;
196	struct task_struct *task;
197	bool up;
198};
199
200/*
201 * Because this function is inlined, the 'state' parameter will be
202 * constant, and thus optimised away by the compiler.  Likewise the
203 * 'timeout' parameter for the cases without timeouts.
204 */
205static inline int __sched __down_common(struct semaphore *sem, long state,
206								long timeout)
207{
208	struct semaphore_waiter waiter;
209
210	list_add_tail(&waiter.list, &sem->wait_list);
211	waiter.task = current;
212	waiter.up = false;
213
214	for (;;) {
215		if (signal_pending_state(state, current))
216			goto interrupted;
217		if (unlikely(timeout <= 0))
218			goto timed_out;
219		__set_current_state(state);
220		raw_spin_unlock_irq(&sem->lock);
221		timeout = schedule_timeout(timeout);
222		raw_spin_lock_irq(&sem->lock);
223		if (waiter.up)
224			return 0;
225	}
226
227 timed_out:
228	list_del(&waiter.list);
229	return -ETIME;
230
231 interrupted:
232	list_del(&waiter.list);
233	return -EINTR;
 
 
 
 
 
 
 
 
 
 
 
 
234}
235
236static noinline void __sched __down(struct semaphore *sem)
237{
238	__down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
239}
240
241static noinline int __sched __down_interruptible(struct semaphore *sem)
242{
243	return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
244}
245
246static noinline int __sched __down_killable(struct semaphore *sem)
247{
248	return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
249}
250
251static noinline int __sched __down_timeout(struct semaphore *sem, long timeout)
252{
253	return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
254}
255
256static noinline void __sched __up(struct semaphore *sem)
257{
258	struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
259						struct semaphore_waiter, list);
260	list_del(&waiter->list);
261	waiter->up = true;
262	wake_up_process(waiter->task);
263}

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (c) 2008 Intel Corporation
  4 * Author: Matthew Wilcox <willy@linux.intel.com>
  5 *
 
 
  6 * This file implements counting semaphores.
  7 * A counting semaphore may be acquired 'n' times before sleeping.
  8 * See mutex.c for single-acquisition sleeping locks which enforce
  9 * rules which allow code to be debugged more easily.
 10 */
 11
 12/*
 13 * Some notes on the implementation:
 14 *
 15 * The spinlock controls access to the other members of the semaphore.
 16 * down_trylock() and up() can be called from interrupt context, so we
 17 * have to disable interrupts when taking the lock.  It turns out various
 18 * parts of the kernel expect to be able to use down() on a semaphore in
 19 * interrupt context when they know it will succeed, so we have to use
 20 * irqsave variants for down(), down_interruptible() and down_killable()
 21 * too.
 22 *
 23 * The ->count variable represents how many more tasks can acquire this
 24 * semaphore.  If it's zero, there may be tasks waiting on the wait_list.
 25 */
 26
 27#include <linux/compiler.h>
 28#include <linux/kernel.h>
 29#include <linux/export.h>
 30#include <linux/sched.h>
 31#include <linux/sched/debug.h>
 32#include <linux/semaphore.h>
 33#include <linux/spinlock.h>
 34#include <linux/ftrace.h>
 35#include <trace/events/lock.h>
 36
 37static noinline void __down(struct semaphore *sem);
 38static noinline int __down_interruptible(struct semaphore *sem);
 39static noinline int __down_killable(struct semaphore *sem);
 40static noinline int __down_timeout(struct semaphore *sem, long timeout);
 41static noinline void __up(struct semaphore *sem);
 42
 43/**
 44 * down - acquire the semaphore
 45 * @sem: the semaphore to be acquired
 46 *
 47 * Acquires the semaphore.  If no more tasks are allowed to acquire the
 48 * semaphore, calling this function will put the task to sleep until the
 49 * semaphore is released.
 50 *
 51 * Use of this function is deprecated, please use down_interruptible() or
 52 * down_killable() instead.
 53 */
 54void __sched down(struct semaphore *sem)
 55{
 56	unsigned long flags;
 57
 58	might_sleep();
 59	raw_spin_lock_irqsave(&sem->lock, flags);
 60	if (likely(sem->count > 0))
 61		sem->count--;
 62	else
 63		__down(sem);
 64	raw_spin_unlock_irqrestore(&sem->lock, flags);
 65}
 66EXPORT_SYMBOL(down);
 67
 68/**
 69 * down_interruptible - acquire the semaphore unless interrupted
 70 * @sem: the semaphore to be acquired
 71 *
 72 * Attempts to acquire the semaphore.  If no more tasks are allowed to
 73 * acquire the semaphore, calling this function will put the task to sleep.
 74 * If the sleep is interrupted by a signal, this function will return -EINTR.
 75 * If the semaphore is successfully acquired, this function returns 0.
 76 */
 77int __sched down_interruptible(struct semaphore *sem)
 78{
 79	unsigned long flags;
 80	int result = 0;
 81
 82	might_sleep();
 83	raw_spin_lock_irqsave(&sem->lock, flags);
 84	if (likely(sem->count > 0))
 85		sem->count--;
 86	else
 87		result = __down_interruptible(sem);
 88	raw_spin_unlock_irqrestore(&sem->lock, flags);
 89
 90	return result;
 91}
 92EXPORT_SYMBOL(down_interruptible);
 93
 94/**
 95 * down_killable - acquire the semaphore unless killed
 96 * @sem: the semaphore to be acquired
 97 *
 98 * Attempts to acquire the semaphore.  If no more tasks are allowed to
 99 * acquire the semaphore, calling this function will put the task to sleep.
100 * If the sleep is interrupted by a fatal signal, this function will return
101 * -EINTR.  If the semaphore is successfully acquired, this function returns
102 * 0.
103 */
104int __sched down_killable(struct semaphore *sem)
105{
106	unsigned long flags;
107	int result = 0;
108
109	might_sleep();
110	raw_spin_lock_irqsave(&sem->lock, flags);
111	if (likely(sem->count > 0))
112		sem->count--;
113	else
114		result = __down_killable(sem);
115	raw_spin_unlock_irqrestore(&sem->lock, flags);
116
117	return result;
118}
119EXPORT_SYMBOL(down_killable);
120
121/**
122 * down_trylock - try to acquire the semaphore, without waiting
123 * @sem: the semaphore to be acquired
124 *
125 * Try to acquire the semaphore atomically.  Returns 0 if the semaphore has
126 * been acquired successfully or 1 if it cannot be acquired.
127 *
128 * NOTE: This return value is inverted from both spin_trylock and
129 * mutex_trylock!  Be careful about this when converting code.
130 *
131 * Unlike mutex_trylock, this function can be used from interrupt context,
132 * and the semaphore can be released by any task or interrupt.
133 */
134int __sched down_trylock(struct semaphore *sem)
135{
136	unsigned long flags;
137	int count;
138
139	raw_spin_lock_irqsave(&sem->lock, flags);
140	count = sem->count - 1;
141	if (likely(count >= 0))
142		sem->count = count;
143	raw_spin_unlock_irqrestore(&sem->lock, flags);
144
145	return (count < 0);
146}
147EXPORT_SYMBOL(down_trylock);
148
149/**
150 * down_timeout - acquire the semaphore within a specified time
151 * @sem: the semaphore to be acquired
152 * @timeout: how long to wait before failing
153 *
154 * Attempts to acquire the semaphore.  If no more tasks are allowed to
155 * acquire the semaphore, calling this function will put the task to sleep.
156 * If the semaphore is not released within the specified number of jiffies,
157 * this function returns -ETIME.  It returns 0 if the semaphore was acquired.
158 */
159int __sched down_timeout(struct semaphore *sem, long timeout)
160{
161	unsigned long flags;
162	int result = 0;
163
164	might_sleep();
165	raw_spin_lock_irqsave(&sem->lock, flags);
166	if (likely(sem->count > 0))
167		sem->count--;
168	else
169		result = __down_timeout(sem, timeout);
170	raw_spin_unlock_irqrestore(&sem->lock, flags);
171
172	return result;
173}
174EXPORT_SYMBOL(down_timeout);
175
176/**
177 * up - release the semaphore
178 * @sem: the semaphore to release
179 *
180 * Release the semaphore.  Unlike mutexes, up() may be called from any
181 * context and even by tasks which have never called down().
182 */
183void __sched up(struct semaphore *sem)
184{
185	unsigned long flags;
186
187	raw_spin_lock_irqsave(&sem->lock, flags);
188	if (likely(list_empty(&sem->wait_list)))
189		sem->count++;
190	else
191		__up(sem);
192	raw_spin_unlock_irqrestore(&sem->lock, flags);
193}
194EXPORT_SYMBOL(up);
195
196/* Functions for the contended case */
197
198struct semaphore_waiter {
199	struct list_head list;
200	struct task_struct *task;
201	bool up;
202};
203
204/*
205 * Because this function is inlined, the 'state' parameter will be
206 * constant, and thus optimised away by the compiler.  Likewise the
207 * 'timeout' parameter for the cases without timeouts.
208 */
209static inline int __sched ___down_common(struct semaphore *sem, long state,
210								long timeout)
211{
212	struct semaphore_waiter waiter;
213
214	list_add_tail(&waiter.list, &sem->wait_list);
215	waiter.task = current;
216	waiter.up = false;
217
218	for (;;) {
219		if (signal_pending_state(state, current))
220			goto interrupted;
221		if (unlikely(timeout <= 0))
222			goto timed_out;
223		__set_current_state(state);
224		raw_spin_unlock_irq(&sem->lock);
225		timeout = schedule_timeout(timeout);
226		raw_spin_lock_irq(&sem->lock);
227		if (waiter.up)
228			return 0;
229	}
230
231 timed_out:
232	list_del(&waiter.list);
233	return -ETIME;
234
235 interrupted:
236	list_del(&waiter.list);
237	return -EINTR;
238}
239
240static inline int __sched __down_common(struct semaphore *sem, long state,
241					long timeout)
242{
243	int ret;
244
245	trace_contention_begin(sem, 0);
246	ret = ___down_common(sem, state, timeout);
247	trace_contention_end(sem, ret);
248
249	return ret;
250}
251
252static noinline void __sched __down(struct semaphore *sem)
253{
254	__down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
255}
256
257static noinline int __sched __down_interruptible(struct semaphore *sem)
258{
259	return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
260}
261
262static noinline int __sched __down_killable(struct semaphore *sem)
263{
264	return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
265}
266
267static noinline int __sched __down_timeout(struct semaphore *sem, long timeout)
268{
269	return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
270}
271
272static noinline void __sched __up(struct semaphore *sem)
273{
274	struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
275						struct semaphore_waiter, list);
276	list_del(&waiter->list);
277	waiter->up = true;
278	wake_up_process(waiter->task);
279}