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![Nicolas Pitre](/assets/img/avatar_default.png)
Patch from Nicolas Pitre We must make sure that assembly code that modifies the stack pointer before calling a C function does it so it remains 64-bit aligned. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
221 lines
5.7 KiB
C
221 lines
5.7 KiB
C
/*
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* ARM semaphore implementation, taken from
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*
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* i386 semaphore implementation.
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*
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* (C) Copyright 1999 Linus Torvalds
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*
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* Modified for ARM by Russell King
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/module.h>
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#include <linux/sched.h>
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#include <linux/errno.h>
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#include <linux/init.h>
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#include <asm/semaphore.h>
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/*
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* Semaphores are implemented using a two-way counter:
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* The "count" variable is decremented for each process
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* that tries to acquire the semaphore, while the "sleeping"
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* variable is a count of such acquires.
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*
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* Notably, the inline "up()" and "down()" functions can
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* efficiently test if they need to do any extra work (up
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* needs to do something only if count was negative before
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* the increment operation.
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*
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* "sleeping" and the contention routine ordering is
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* protected by the semaphore spinlock.
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*
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* Note that these functions are only called when there is
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* contention on the lock, and as such all this is the
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* "non-critical" part of the whole semaphore business. The
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* critical part is the inline stuff in <asm/semaphore.h>
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* where we want to avoid any extra jumps and calls.
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*/
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/*
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* Logic:
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* - only on a boundary condition do we need to care. When we go
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* from a negative count to a non-negative, we wake people up.
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* - when we go from a non-negative count to a negative do we
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* (a) synchronize with the "sleeper" count and (b) make sure
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* that we're on the wakeup list before we synchronize so that
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* we cannot lose wakeup events.
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*/
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void __up(struct semaphore *sem)
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{
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wake_up(&sem->wait);
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}
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static DEFINE_SPINLOCK(semaphore_lock);
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void __sched __down(struct semaphore * sem)
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{
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struct task_struct *tsk = current;
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DECLARE_WAITQUEUE(wait, tsk);
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tsk->state = TASK_UNINTERRUPTIBLE;
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add_wait_queue_exclusive(&sem->wait, &wait);
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spin_lock_irq(&semaphore_lock);
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sem->sleepers++;
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for (;;) {
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int sleepers = sem->sleepers;
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/*
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* Add "everybody else" into it. They aren't
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* playing, because we own the spinlock.
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*/
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if (!atomic_add_negative(sleepers - 1, &sem->count)) {
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sem->sleepers = 0;
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break;
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}
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sem->sleepers = 1; /* us - see -1 above */
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spin_unlock_irq(&semaphore_lock);
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schedule();
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tsk->state = TASK_UNINTERRUPTIBLE;
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spin_lock_irq(&semaphore_lock);
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}
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spin_unlock_irq(&semaphore_lock);
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remove_wait_queue(&sem->wait, &wait);
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tsk->state = TASK_RUNNING;
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wake_up(&sem->wait);
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}
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int __sched __down_interruptible(struct semaphore * sem)
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{
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int retval = 0;
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struct task_struct *tsk = current;
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DECLARE_WAITQUEUE(wait, tsk);
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tsk->state = TASK_INTERRUPTIBLE;
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add_wait_queue_exclusive(&sem->wait, &wait);
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spin_lock_irq(&semaphore_lock);
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sem->sleepers ++;
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for (;;) {
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int sleepers = sem->sleepers;
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/*
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* With signals pending, this turns into
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* the trylock failure case - we won't be
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* sleeping, and we* can't get the lock as
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* it has contention. Just correct the count
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* and exit.
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*/
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if (signal_pending(current)) {
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retval = -EINTR;
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sem->sleepers = 0;
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atomic_add(sleepers, &sem->count);
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break;
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}
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/*
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* Add "everybody else" into it. They aren't
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* playing, because we own the spinlock. The
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* "-1" is because we're still hoping to get
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* the lock.
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*/
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if (!atomic_add_negative(sleepers - 1, &sem->count)) {
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sem->sleepers = 0;
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break;
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}
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sem->sleepers = 1; /* us - see -1 above */
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spin_unlock_irq(&semaphore_lock);
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schedule();
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tsk->state = TASK_INTERRUPTIBLE;
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spin_lock_irq(&semaphore_lock);
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}
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spin_unlock_irq(&semaphore_lock);
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tsk->state = TASK_RUNNING;
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remove_wait_queue(&sem->wait, &wait);
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wake_up(&sem->wait);
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return retval;
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}
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/*
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* Trylock failed - make sure we correct for
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* having decremented the count.
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*
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* We could have done the trylock with a
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* single "cmpxchg" without failure cases,
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* but then it wouldn't work on a 386.
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*/
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int __down_trylock(struct semaphore * sem)
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{
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int sleepers;
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unsigned long flags;
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spin_lock_irqsave(&semaphore_lock, flags);
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sleepers = sem->sleepers + 1;
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sem->sleepers = 0;
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/*
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* Add "everybody else" and us into it. They aren't
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* playing, because we own the spinlock.
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*/
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if (!atomic_add_negative(sleepers, &sem->count))
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wake_up(&sem->wait);
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spin_unlock_irqrestore(&semaphore_lock, flags);
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return 1;
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}
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/*
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* The semaphore operations have a special calling sequence that
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* allow us to do a simpler in-line version of them. These routines
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* need to convert that sequence back into the C sequence when
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* there is contention on the semaphore.
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*
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* ip contains the semaphore pointer on entry. Save the C-clobbered
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* registers (r0 to r3 and lr), but not ip, as we use it as a return
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* value in some cases..
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* To remain AAPCS compliant (64-bit stack align) we save r4 as well.
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*/
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asm(" .section .sched.text,\"ax\",%progbits \n\
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.align 5 \n\
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.globl __down_failed \n\
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__down_failed: \n\
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stmfd sp!, {r0 - r4, lr} \n\
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mov r0, ip \n\
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bl __down \n\
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ldmfd sp!, {r0 - r4, pc} \n\
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\n\
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.align 5 \n\
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.globl __down_interruptible_failed \n\
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__down_interruptible_failed: \n\
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stmfd sp!, {r0 - r4, lr} \n\
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mov r0, ip \n\
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bl __down_interruptible \n\
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mov ip, r0 \n\
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ldmfd sp!, {r0 - r4, pc} \n\
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\n\
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.align 5 \n\
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.globl __down_trylock_failed \n\
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__down_trylock_failed: \n\
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stmfd sp!, {r0 - r4, lr} \n\
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mov r0, ip \n\
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bl __down_trylock \n\
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mov ip, r0 \n\
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ldmfd sp!, {r0 - r4, pc} \n\
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\n\
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.align 5 \n\
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.globl __up_wakeup \n\
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__up_wakeup: \n\
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stmfd sp!, {r0 - r4, lr} \n\
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mov r0, ip \n\
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bl __up \n\
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ldmfd sp!, {r0 - r4, pc} \n\
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");
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EXPORT_SYMBOL(__down_failed);
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EXPORT_SYMBOL(__down_interruptible_failed);
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EXPORT_SYMBOL(__down_trylock_failed);
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EXPORT_SYMBOL(__up_wakeup);
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