From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 16 Apr 2005 15:20:36 -0700 Subject: Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip! --- arch/i386/kernel/semaphore.c | 297 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 297 insertions(+) create mode 100644 arch/i386/kernel/semaphore.c (limited to 'arch/i386/kernel/semaphore.c') diff --git a/arch/i386/kernel/semaphore.c b/arch/i386/kernel/semaphore.c new file mode 100644 index 00000000000..469f496e55c --- /dev/null +++ b/arch/i386/kernel/semaphore.c @@ -0,0 +1,297 @@ +/* + * i386 semaphore implementation. + * + * (C) Copyright 1999 Linus Torvalds + * + * Portions Copyright 1999 Red Hat, Inc. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + * + * 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 + * need to convert that sequence back into the C sequence when + * there is contention on the semaphore. + * + * %eax contains the semaphore pointer on entry. Save the C-clobbered + * registers (%eax, %edx and %ecx) except %eax whish is either a return + * value or just clobbered.. + */ +asm( +".section .sched.text\n" +".align 4\n" +".globl __down_failed\n" +"__down_failed:\n\t" +#if defined(CONFIG_FRAME_POINTER) + "pushl %ebp\n\t" + "movl %esp,%ebp\n\t" +#endif + "pushl %edx\n\t" + "pushl %ecx\n\t" + "call __down\n\t" + "popl %ecx\n\t" + "popl %edx\n\t" +#if defined(CONFIG_FRAME_POINTER) + "movl %ebp,%esp\n\t" + "popl %ebp\n\t" +#endif + "ret" +); + +asm( +".section .sched.text\n" +".align 4\n" +".globl __down_failed_interruptible\n" +"__down_failed_interruptible:\n\t" +#if defined(CONFIG_FRAME_POINTER) + "pushl %ebp\n\t" + "movl %esp,%ebp\n\t" +#endif + "pushl %edx\n\t" + "pushl %ecx\n\t" + "call __down_interruptible\n\t" + "popl %ecx\n\t" + "popl %edx\n\t" +#if defined(CONFIG_FRAME_POINTER) + "movl %ebp,%esp\n\t" + "popl %ebp\n\t" +#endif + "ret" +); + +asm( +".section .sched.text\n" +".align 4\n" +".globl __down_failed_trylock\n" +"__down_failed_trylock:\n\t" +#if defined(CONFIG_FRAME_POINTER) + "pushl %ebp\n\t" + "movl %esp,%ebp\n\t" +#endif + "pushl %edx\n\t" + "pushl %ecx\n\t" + "call __down_trylock\n\t" + "popl %ecx\n\t" + "popl %edx\n\t" +#if defined(CONFIG_FRAME_POINTER) + "movl %ebp,%esp\n\t" + "popl %ebp\n\t" +#endif + "ret" +); + +asm( +".section .sched.text\n" +".align 4\n" +".globl __up_wakeup\n" +"__up_wakeup:\n\t" + "pushl %edx\n\t" + "pushl %ecx\n\t" + "call __up\n\t" + "popl %ecx\n\t" + "popl %edx\n\t" + "ret" +); + +/* + * rw spinlock fallbacks + */ +#if defined(CONFIG_SMP) +asm( +".section .sched.text\n" +".align 4\n" +".globl __write_lock_failed\n" +"__write_lock_failed:\n\t" + LOCK "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" + "jnz __write_lock_failed\n\t" + "ret" +); + +asm( +".section .sched.text\n" +".align 4\n" +".globl __read_lock_failed\n" +"__read_lock_failed:\n\t" + LOCK "incl (%eax)\n" +"1: rep; nop\n\t" + "cmpl $1,(%eax)\n\t" + "js 1b\n\t" + LOCK "decl (%eax)\n\t" + "js __read_lock_failed\n\t" + "ret" +); +#endif -- cgit v1.2.3-70-g09d2