diff options
| -rw-r--r-- | include/linux/semaphore.h | 39 | ||||
| -rw-r--r-- | kernel/semaphore.c | 79 |
2 files changed, 70 insertions, 48 deletions
diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index a7125da..9cae64b 100644 --- a/include/linux/semaphore.h +++ b/include/linux/semaphore.h @@ -4,8 +4,7 @@ * * Distributed under the terms of the GNU GPL, version 2 * - * Counting semaphores allow up to <n> tasks to acquire the semaphore - * simultaneously. + * Please see kernel/semaphore.c for documentation of these functions */ #ifndef __LINUX_SEMAPHORE_H #define __LINUX_SEMAPHORE_H @@ -13,11 +12,7 @@ #include <linux/list.h> #include <linux/spinlock.h> -/* - * The spinlock controls access to the other members of the semaphore. - * 'count' represents how many more tasks can acquire this semaphore. - * Tasks waiting for the lock are kept on the wait_list. - */ +/* Please don't access any members of this structure directly */ struct semaphore { spinlock_t lock; unsigned int count; @@ -46,41 +41,11 @@ static inline void sema_init(struct semaphore *sem, int val) #define init_MUTEX(sem) sema_init(sem, 1) #define init_MUTEX_LOCKED(sem) sema_init(sem, 0) -/* - * Attempt to acquire the semaphore. If another task is already holding the - * semaphore, sleep until the semaphore is released. - */ extern void down(struct semaphore *sem); - -/* - * As down(), except the sleep may be interrupted by a signal. If it is, - * this function will return -EINTR. - */ extern int __must_check down_interruptible(struct semaphore *sem); - -/* - * As down_interruptible(), except the sleep may only be interrupted by - * signals which are fatal to this process. - */ extern int __must_check down_killable(struct semaphore *sem); - -/* - * As down(), except this function will not sleep. It will return 0 if it - * acquired the semaphore and 1 if the semaphore was contended. This - * function may be called from any context, including interrupt and softirq. - */ extern int __must_check down_trylock(struct semaphore *sem); - -/* - * As down(), except this function will return -ETIME if it fails to - * acquire the semaphore within the specified number of jiffies. - */ extern int __must_check down_timeout(struct semaphore *sem, long jiffies); - -/* - * Release the semaphore. Unlike mutexes, up() may be called from any - * context and even by tasks which have never called down(). - */ extern void up(struct semaphore *sem); #endif /* __LINUX_SEMAPHORE_H */ diff --git a/kernel/semaphore.c b/kernel/semaphore.c index bef977b..5c2942e 100644 --- a/kernel/semaphore.c +++ b/kernel/semaphore.c @@ -3,6 +3,26 @@ * Author: Matthew Wilcox <willy@linux.intel.com> * * 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 <linux/compiler.h> @@ -12,22 +32,23 @@ #include <linux/semaphore.h> #include <linux/spinlock.h> -/* - * Some notes on the implementation: - * - * down_trylock() and up() can be called from interrupt context. - * So we have to disable interrupts when taking the lock. - * - * The ->count variable defines how many more tasks can acquire the - * semaphore. If it's zero, there may be tasks waiting on the list. - */ - 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 jiffies); 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; @@ -41,6 +62,15 @@ void down(struct semaphore *sem) } 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; @@ -57,6 +87,16 @@ int down_interruptible(struct semaphore *sem) } 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; @@ -78,7 +118,7 @@ EXPORT_SYMBOL(down_killable); * @sem: the semaphore to be acquired * * Try to acquire the semaphore atomically. Returns 0 if the mutex has - * been acquired successfully and 1 if it is contended. + * 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. @@ -101,6 +141,16 @@ int down_trylock(struct semaphore *sem) } EXPORT_SYMBOL(down_trylock); +/** + * down_timeout - acquire the semaphore within a specified time + * @sem: the semaphore to be acquired + * @jiffies: 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 jiffies) { unsigned long flags; @@ -117,6 +167,13 @@ int down_timeout(struct semaphore *sem, long jiffies) } 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; |