From 8b91de2e58318d1168bc13d164478c1a7217a63a Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Tue, 26 Feb 2008 09:53:20 -0500 Subject: Fix quota.h includes quota.h currently relies on asm/semaphore.h (through some chain; it doesn't actually include semaphore.h itself) to include wait.h. As well as being bad practice to rely on an implicit include, subsequent patches will break this. While I'm in this file, add atomic.h and list.h, and sort the list of includes. Signed-off-by: Matthew Wilcox --- include/linux/quota.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/quota.h b/include/linux/quota.h index 6e0393a5b2ea..eb560d031acd 100644 --- a/include/linux/quota.h +++ b/include/linux/quota.h @@ -160,14 +160,18 @@ enum { #ifdef __KERNEL__ -#include -#include +#include #include +#include +#include +#include #include #include #include +#include + extern spinlock_t dq_data_lock; /* Maximal numbers of writes for quota operation (insert/delete/update) -- cgit v1.2.3 From 64ac24e738823161693bf791f87adc802cf529ff Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Fri, 7 Mar 2008 21:55:58 -0500 Subject: Generic semaphore implementation Semaphores are no longer performance-critical, so a generic C implementation is better for maintainability, debuggability and extensibility. Thanks to Peter Zijlstra for fixing the lockdep warning. Thanks to Harvey Harrison for pointing out that the unlikely() was unnecessary. Signed-off-by: Matthew Wilcox Acked-by: Ingo Molnar --- include/linux/semaphore.h | 77 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 77 insertions(+) create mode 100644 include/linux/semaphore.h (limited to 'include/linux') diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h new file mode 100644 index 000000000000..b3c691b089b2 --- /dev/null +++ b/include/linux/semaphore.h @@ -0,0 +1,77 @@ +/* + * Copyright (c) 2008 Intel Corporation + * Author: Matthew Wilcox + * + * Distributed under the terms of the GNU GPL, version 2 + * + * Counting semaphores allow up to tasks to acquire the semaphore + * simultaneously. + */ +#ifndef __LINUX_SEMAPHORE_H +#define __LINUX_SEMAPHORE_H + +#include +#include + +/* + * The spinlock controls access to the other members of the semaphore. + * 'count' is decremented by every task which calls down*() and incremented + * by every call to up(). Thus, if it is positive, it indicates how many + * more tasks may acquire the lock. If it is negative, it indicates how + * many tasks are waiting for the lock. Tasks waiting for the lock are + * kept on the wait_list. + */ +struct semaphore { + spinlock_t lock; + int count; + struct list_head wait_list; +}; + +#define __SEMAPHORE_INITIALIZER(name, n) \ +{ \ + .lock = __SPIN_LOCK_UNLOCKED((name).lock), \ + .count = n, \ + .wait_list = LIST_HEAD_INIT((name).wait_list), \ +} + +#define __DECLARE_SEMAPHORE_GENERIC(name, count) \ + struct semaphore name = __SEMAPHORE_INITIALIZER(name, count) + +#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1) + +static inline void sema_init(struct semaphore *sem, int val) +{ + static struct lock_class_key __key; + *sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val); + lockdep_init_map(&sem->lock.dep_map, "semaphore->lock", &__key, 0); +} + +#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(), 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); + +/* + * 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 */ -- cgit v1.2.3 From f06d96865861c3dd01520f47e2e61c899db1631f Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Fri, 14 Mar 2008 13:19:33 -0400 Subject: Introduce down_killable() down_killable() is the functional counterpart of mutex_lock_killable. Signed-off-by: Matthew Wilcox --- include/linux/semaphore.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include/linux') diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index b3c691b089b2..88f2a28cc0f1 100644 --- a/include/linux/semaphore.h +++ b/include/linux/semaphore.h @@ -61,6 +61,12 @@ extern void down(struct semaphore *sem); */ 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 -- cgit v1.2.3 From f1241c87a16c4fe9f4f51d6ed3589f031c505e8d Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Fri, 14 Mar 2008 13:43:13 -0400 Subject: Add down_timeout and change ACPI to use it ACPI currently emulates a timeout for semaphores with calls to down_trylock and sleep. This produces horrible behaviour in terms of fairness and excessive wakeups. Now that we have a unified semaphore implementation, adding a real down_trylock is almost trivial. Signed-off-by: Matthew Wilcox --- include/linux/semaphore.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include/linux') diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index 88f2a28cc0f1..a107aebd9148 100644 --- a/include/linux/semaphore.h +++ b/include/linux/semaphore.h @@ -74,6 +74,12 @@ extern int __must_check down_killable(struct semaphore *sem); */ 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(). -- cgit v1.2.3 From b17170b2fac96705db3188f093f89e8e838418e4 Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Fri, 14 Mar 2008 14:35:22 -0400 Subject: Simplify semaphore implementation By removing the negative values of 'count' and relying on the wait_list to indicate whether we have any waiters, we can simplify the implementation by removing the protection against an unlikely race condition. Thanks to David Howells for his suggestions. Signed-off-by: Matthew Wilcox --- include/linux/semaphore.h | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) (limited to 'include/linux') diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index a107aebd9148..a7125daaff90 100644 --- a/include/linux/semaphore.h +++ b/include/linux/semaphore.h @@ -15,15 +15,12 @@ /* * The spinlock controls access to the other members of the semaphore. - * 'count' is decremented by every task which calls down*() and incremented - * by every call to up(). Thus, if it is positive, it indicates how many - * more tasks may acquire the lock. If it is negative, it indicates how - * many tasks are waiting for the lock. Tasks waiting for the lock are - * kept on the wait_list. + * 'count' represents how many more tasks can acquire this semaphore. + * Tasks waiting for the lock are kept on the wait_list. */ struct semaphore { spinlock_t lock; - int count; + unsigned int count; struct list_head wait_list; }; -- cgit v1.2.3 From 714493cd5468f42ca3c4f730a9c17c203abd5059 Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Fri, 11 Apr 2008 15:23:52 -0400 Subject: Improve semaphore documentation Move documentation from semaphore.h to semaphore.c as requested by Andrew Morton. Also reformat to kernel-doc style and add some more notes about the implementation. Signed-off-by: Matthew Wilcox --- include/linux/semaphore.h | 39 ++------------------------------------- 1 file changed, 2 insertions(+), 37 deletions(-) (limited to 'include/linux') diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h index a7125daaff90..9cae64b00d6b 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 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 #include -/* - * 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 */ -- cgit v1.2.3