X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=arch%2Fi386%2Fkernel%2Fsemaphore.c;h=967dc74df9eeb69750077eaf783bc5af587788a4;hb=43bc926fffd92024b46cafaf7350d669ba9ca884;hp=469f496e55c0f56787929fa1c387572097c9ddc8;hpb=cee37fe97739d85991964371c1f3a745c00dd236;p=linux-2.6.git diff --git a/arch/i386/kernel/semaphore.c b/arch/i386/kernel/semaphore.c index 469f496e5..967dc74df 100644 --- a/arch/i386/kernel/semaphore.c +++ b/arch/i386/kernel/semaphore.c @@ -13,170 +13,8 @@ * rw semaphores implemented November 1999 by Benjamin LaHaise */ #include -#include -#include -#include #include -/* - * Semaphores are implemented using a two-way counter: - * The "count" variable is decremented for each process - * that tries to acquire the semaphore, while the "sleeping" - * variable is a count of such acquires. - * - * 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. - * - * "sleeping" and the contention routine ordering is protected - * by the spinlock in the semaphore's waitqueue head. - * - * 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. - */ - -/* - * Logic: - * - only on a boundary condition do we need to care. When we go - * from a negative count to a non-negative, we wake people up. - * - when we go from a non-negative count to a negative do we - * (a) synchronize with the "sleeper" count and (b) make sure - * that we're on the wakeup list before we synchronize so that - * we cannot lose wakeup events. - */ - -static fastcall void __attribute_used__ __up(struct semaphore *sem) -{ - wake_up(&sem->wait); -} - -static fastcall void __attribute_used__ __sched __down(struct semaphore * sem) -{ - struct task_struct *tsk = current; - DECLARE_WAITQUEUE(wait, tsk); - unsigned long flags; - - tsk->state = TASK_UNINTERRUPTIBLE; - spin_lock_irqsave(&sem->wait.lock, flags); - add_wait_queue_exclusive_locked(&sem->wait, &wait); - - sem->sleepers++; - for (;;) { - int sleepers = sem->sleepers; - - /* - * Add "everybody else" into it. They aren't - * playing, because we own the spinlock in - * the wait_queue_head. - */ - if (!atomic_add_negative(sleepers - 1, &sem->count)) { - sem->sleepers = 0; - break; - } - sem->sleepers = 1; /* us - see -1 above */ - spin_unlock_irqrestore(&sem->wait.lock, flags); - - schedule(); - - spin_lock_irqsave(&sem->wait.lock, flags); - tsk->state = TASK_UNINTERRUPTIBLE; - } - remove_wait_queue_locked(&sem->wait, &wait); - wake_up_locked(&sem->wait); - spin_unlock_irqrestore(&sem->wait.lock, flags); - tsk->state = TASK_RUNNING; -} - -static fastcall int __attribute_used__ __sched __down_interruptible(struct semaphore * sem) -{ - int retval = 0; - struct task_struct *tsk = current; - DECLARE_WAITQUEUE(wait, tsk); - unsigned long flags; - - tsk->state = TASK_INTERRUPTIBLE; - spin_lock_irqsave(&sem->wait.lock, flags); - add_wait_queue_exclusive_locked(&sem->wait, &wait); - - sem->sleepers++; - for (;;) { - int sleepers = sem->sleepers; - - /* - * With signals pending, this turns into - * the trylock failure case - we won't be - * sleeping, and we* can't get the lock as - * it has contention. Just correct the count - * and exit. - */ - if (signal_pending(current)) { - retval = -EINTR; - sem->sleepers = 0; - atomic_add(sleepers, &sem->count); - break; - } - - /* - * Add "everybody else" into it. They aren't - * playing, because we own the spinlock in - * wait_queue_head. The "-1" is because we're - * still hoping to get the semaphore. - */ - if (!atomic_add_negative(sleepers - 1, &sem->count)) { - sem->sleepers = 0; - break; - } - sem->sleepers = 1; /* us - see -1 above */ - spin_unlock_irqrestore(&sem->wait.lock, flags); - - schedule(); - - spin_lock_irqsave(&sem->wait.lock, flags); - tsk->state = TASK_INTERRUPTIBLE; - } - remove_wait_queue_locked(&sem->wait, &wait); - wake_up_locked(&sem->wait); - spin_unlock_irqrestore(&sem->wait.lock, flags); - - tsk->state = TASK_RUNNING; - return retval; -} - -/* - * Trylock failed - make sure we correct for - * having decremented the count. - * - * We could have done the trylock with a - * single "cmpxchg" without failure cases, - * but then it wouldn't work on a 386. - */ -static fastcall int __attribute_used__ __down_trylock(struct semaphore * sem) -{ - int sleepers; - unsigned long flags; - - spin_lock_irqsave(&sem->wait.lock, flags); - sleepers = sem->sleepers + 1; - sem->sleepers = 0; - - /* - * Add "everybody else" and us into it. They aren't - * playing, because we own the spinlock in the - * wait_queue_head. - */ - if (!atomic_add_negative(sleepers, &sem->count)) { - wake_up_locked(&sem->wait); - } - - spin_unlock_irqrestore(&sem->wait.lock, flags); - return 1; -} - - /* * The semaphore operations have a special calling sequence that * allow us to do a simpler in-line version of them. These routines @@ -272,11 +110,11 @@ asm( ".align 4\n" ".globl __write_lock_failed\n" "__write_lock_failed:\n\t" - LOCK "addl $" RW_LOCK_BIAS_STR ",(%eax)\n" + LOCK_PREFIX "addl $" RW_LOCK_BIAS_STR ",(%eax)\n" "1: rep; nop\n\t" "cmpl $" RW_LOCK_BIAS_STR ",(%eax)\n\t" "jne 1b\n\t" - LOCK "subl $" RW_LOCK_BIAS_STR ",(%eax)\n\t" + LOCK_PREFIX "subl $" RW_LOCK_BIAS_STR ",(%eax)\n\t" "jnz __write_lock_failed\n\t" "ret" ); @@ -286,11 +124,11 @@ asm( ".align 4\n" ".globl __read_lock_failed\n" "__read_lock_failed:\n\t" - LOCK "incl (%eax)\n" + LOCK_PREFIX "incl (%eax)\n" "1: rep; nop\n\t" "cmpl $1,(%eax)\n\t" "js 1b\n\t" - LOCK "decl (%eax)\n\t" + LOCK_PREFIX "decl (%eax)\n\t" "js __read_lock_failed\n\t" "ret" );