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 --- arch/cris/kernel/Makefile | 3 +- arch/cris/kernel/crisksyms.c | 7 --- arch/cris/kernel/semaphore.c | 129 ------------------------------------------- 3 files changed, 1 insertion(+), 138 deletions(-) delete mode 100644 arch/cris/kernel/semaphore.c (limited to 'arch/cris/kernel') diff --git a/arch/cris/kernel/Makefile b/arch/cris/kernel/Makefile index c8e8ea57098..ee7bcd4d20b 100644 --- a/arch/cris/kernel/Makefile +++ b/arch/cris/kernel/Makefile @@ -5,8 +5,7 @@ extra-y := vmlinux.lds -obj-y := process.o traps.o irq.o ptrace.o setup.o \ - time.o sys_cris.o semaphore.o +obj-y := process.o traps.o irq.o ptrace.o setup.o time.o sys_cris.o obj-$(CONFIG_MODULES) += crisksyms.o obj-$(CONFIG_MODULES) += module.o diff --git a/arch/cris/kernel/crisksyms.c b/arch/cris/kernel/crisksyms.c index 62f0e752915..7ac000f6a88 100644 --- a/arch/cris/kernel/crisksyms.c +++ b/arch/cris/kernel/crisksyms.c @@ -9,7 +9,6 @@ #include #include -#include #include #include #include @@ -49,12 +48,6 @@ EXPORT_SYMBOL(__negdi2); EXPORT_SYMBOL(__ioremap); EXPORT_SYMBOL(iounmap); -/* Semaphore functions */ -EXPORT_SYMBOL(__up); -EXPORT_SYMBOL(__down); -EXPORT_SYMBOL(__down_interruptible); -EXPORT_SYMBOL(__down_trylock); - /* Userspace access functions */ EXPORT_SYMBOL(__copy_user_zeroing); EXPORT_SYMBOL(__copy_user); diff --git a/arch/cris/kernel/semaphore.c b/arch/cris/kernel/semaphore.c deleted file mode 100644 index f137a439041..00000000000 --- a/arch/cris/kernel/semaphore.c +++ /dev/null @@ -1,129 +0,0 @@ -/* - * Generic semaphore code. Buyer beware. Do your own - * specific changes in - */ - -#include -#include - -/* - * Semaphores are implemented using a two-way counter: - * The "count" variable is decremented for each process - * that tries to sleep, while the "waking" variable is - * incremented when the "up()" code goes to wake up waiting - * processes. - * - * Notably, the inline "up()" and "down()" functions can - * efficiently test if they need to do any extra work (up - * needs to do something only if count was negative before - * the increment operation. - * - * waking_non_zero() (from asm/semaphore.h) must execute - * atomically. - * - * When __up() is called, the count was negative before - * incrementing it, and we need to wake up somebody. - * - * This routine adds one to the count of processes that need to - * wake up and exit. ALL waiting processes actually wake up but - * only the one that gets to the "waking" field first will gate - * through and acquire the semaphore. The others will go back - * to sleep. - * - * Note that these functions are only called when there is - * contention on the lock, and as such all this is the - * "non-critical" part of the whole semaphore business. The - * critical part is the inline stuff in - * where we want to avoid any extra jumps and calls. - */ -void __up(struct semaphore *sem) -{ - wake_one_more(sem); - wake_up(&sem->wait); -} - -/* - * Perform the "down" function. Return zero for semaphore acquired, - * return negative for signalled out of the function. - * - * If called from __down, the return is ignored and the wait loop is - * not interruptible. This means that a task waiting on a semaphore - * using "down()" cannot be killed until someone does an "up()" on - * the semaphore. - * - * If called from __down_interruptible, the return value gets checked - * upon return. If the return value is negative then the task continues - * with the negative value in the return register (it can be tested by - * the caller). - * - * Either form may be used in conjunction with "up()". - * - */ - -#define DOWN_VAR \ - struct task_struct *tsk = current; \ - wait_queue_t wait; \ - init_waitqueue_entry(&wait, tsk); - -#define DOWN_HEAD(task_state) \ - \ - \ - tsk->state = (task_state); \ - add_wait_queue(&sem->wait, &wait); \ - \ - /* \ - * Ok, we're set up. sem->count is known to be less than zero \ - * so we must wait. \ - * \ - * We can let go the lock for purposes of waiting. \ - * We re-acquire it after awaking so as to protect \ - * all semaphore operations. \ - * \ - * If "up()" is called before we call waking_non_zero() then \ - * we will catch it right away. If it is called later then \ - * we will have to go through a wakeup cycle to catch it. \ - * \ - * Multiple waiters contend for the semaphore lock to see \ - * who gets to gate through and who has to wait some more. \ - */ \ - for (;;) { - -#define DOWN_TAIL(task_state) \ - tsk->state = (task_state); \ - } \ - tsk->state = TASK_RUNNING; \ - remove_wait_queue(&sem->wait, &wait); - -void __sched __down(struct semaphore * sem) -{ - DOWN_VAR - DOWN_HEAD(TASK_UNINTERRUPTIBLE) - if (waking_non_zero(sem)) - break; - schedule(); - DOWN_TAIL(TASK_UNINTERRUPTIBLE) -} - -int __sched __down_interruptible(struct semaphore * sem) -{ - int ret = 0; - DOWN_VAR - DOWN_HEAD(TASK_INTERRUPTIBLE) - - ret = waking_non_zero_interruptible(sem, tsk); - if (ret) - { - if (ret == 1) - /* ret != 0 only if we get interrupted -arca */ - ret = 0; - break; - } - schedule(); - DOWN_TAIL(TASK_INTERRUPTIBLE) - return ret; -} - -int __down_trylock(struct semaphore * sem) -{ - return waking_non_zero_trylock(sem); -} -- cgit v1.2.3