Commit 64ac24e7 authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Matthew Wilcox

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: default avatarMatthew Wilcox <willy@linux.intel.com>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
parent e48b3dee
......@@ -7,7 +7,7 @@ EXTRA_AFLAGS := $(KBUILD_CFLAGS)
EXTRA_CFLAGS := -Werror -Wno-sign-compare
obj-y := entry.o traps.o process.o init_task.o osf_sys.o irq.o \
irq_alpha.o signal.o setup.o ptrace.o time.o semaphore.o \
irq_alpha.o signal.o setup.o ptrace.o time.o \
alpha_ksyms.o systbls.o err_common.o io.o
obj-$(CONFIG_VGA_HOSE) += console.o
......
......@@ -77,15 +77,6 @@ EXPORT_SYMBOL(__do_clear_user);
EXPORT_SYMBOL(__strncpy_from_user);
EXPORT_SYMBOL(__strnlen_user);
/* Semaphore helper functions. */
EXPORT_SYMBOL(__down_failed);
EXPORT_SYMBOL(__down_failed_interruptible);
EXPORT_SYMBOL(__up_wakeup);
EXPORT_SYMBOL(down);
EXPORT_SYMBOL(down_interruptible);
EXPORT_SYMBOL(down_trylock);
EXPORT_SYMBOL(up);
/*
* SMP-specific symbols.
*/
......
/*
* Alpha semaphore implementation.
*
* (C) Copyright 1996 Linus Torvalds
* (C) Copyright 1999, 2000 Richard Henderson
*/
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/init.h>
/*
* This is basically the PPC semaphore scheme ported to use
* the Alpha ll/sc sequences, so see the PPC code for
* credits.
*/
/*
* Atomically update sem->count.
* This does the equivalent of the following:
*
* old_count = sem->count;
* tmp = MAX(old_count, 0) + incr;
* sem->count = tmp;
* return old_count;
*/
static inline int __sem_update_count(struct semaphore *sem, int incr)
{
long old_count, tmp = 0;
__asm__ __volatile__(
"1: ldl_l %0,%2\n"
" cmovgt %0,%0,%1\n"
" addl %1,%3,%1\n"
" stl_c %1,%2\n"
" beq %1,2f\n"
" mb\n"
".subsection 2\n"
"2: br 1b\n"
".previous"
: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
: "Ir" (incr), "1" (tmp), "m" (sem->count));
return old_count;
}
/*
* 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()".
*/
void __sched
__down_failed(struct semaphore *sem)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down failed(%p)\n",
tsk->comm, task_pid_nr(tsk), sem);
#endif
tsk->state = TASK_UNINTERRUPTIBLE;
wmb();
add_wait_queue_exclusive(&sem->wait, &wait);
/*
* Try to get the semaphore. If the count is > 0, then we've
* got the semaphore; we decrement count and exit the loop.
* If the count is 0 or negative, we set it to -1, indicating
* that we are asleep, and then sleep.
*/
while (__sem_update_count(sem, -1) <= 0) {
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
remove_wait_queue(&sem->wait, &wait);
tsk->state = TASK_RUNNING;
/*
* If there are any more sleepers, wake one of them up so
* that it can either get the semaphore, or set count to -1
* indicating that there are still processes sleeping.
*/
wake_up(&sem->wait);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down acquired(%p)\n",
tsk->comm, task_pid_nr(tsk), sem);
#endif
}
int __sched
__down_failed_interruptible(struct semaphore *sem)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
long ret = 0;
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down failed(%p)\n",
tsk->comm, task_pid_nr(tsk), sem);
#endif
tsk->state = TASK_INTERRUPTIBLE;
wmb();
add_wait_queue_exclusive(&sem->wait, &wait);
while (__sem_update_count(sem, -1) <= 0) {
if (signal_pending(current)) {
/*
* A signal is pending - give up trying.
* Set sem->count to 0 if it is negative,
* since we are no longer sleeping.
*/
__sem_update_count(sem, 0);
ret = -EINTR;
break;
}
schedule();
set_task_state(tsk, TASK_INTERRUPTIBLE);
}
remove_wait_queue(&sem->wait, &wait);
tsk->state = TASK_RUNNING;
wake_up(&sem->wait);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down %s(%p)\n",
current->comm, task_pid_nr(current),
(ret < 0 ? "interrupted" : "acquired"), sem);
#endif
return ret;
}
void
__up_wakeup(struct semaphore *sem)
{
/*
* Note that we incremented count in up() before we came here,
* but that was ineffective since the result was <= 0, and
* any negative value of count is equivalent to 0.
* This ends up setting count to 1, unless count is now > 0
* (i.e. because some other cpu has called up() in the meantime),
* in which case we just increment count.
*/
__sem_update_count(sem, 1);
wake_up(&sem->wait);
}
void __sched
down(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down(%p) <count=%d> from %p\n",
current->comm, task_pid_nr(current), sem,
atomic_read(&sem->count), __builtin_return_address(0));
#endif
__down(sem);
}
int __sched
down_interruptible(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down(%p) <count=%d> from %p\n",
current->comm, task_pid_nr(current), sem,
atomic_read(&sem->count), __builtin_return_address(0));
#endif
return __down_interruptible(sem);
}
int
down_trylock(struct semaphore *sem)
{
int ret;
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
ret = __down_trylock(sem);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down_trylock %s from %p\n",
current->comm, task_pid_nr(current),
ret ? "failed" : "acquired",
__builtin_return_address(0));
#endif
return ret;
}
void
up(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): up(%p) <count=%d> from %p\n",
current->comm, task_pid_nr(current), sem,
atomic_read(&sem->count), __builtin_return_address(0));
#endif
__up(sem);
}
......@@ -7,7 +7,7 @@ AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
# Object file lists.
obj-y := compat.o entry-armv.o entry-common.o irq.o \
process.o ptrace.o semaphore.o setup.o signal.o \
process.o ptrace.o setup.o signal.o \
sys_arm.o stacktrace.o time.o traps.o
obj-$(CONFIG_ISA_DMA_API) += dma.o
......
/*
* ARM semaphore implementation, taken from
*
* i386 semaphore implementation.
*
* (C) Copyright 1999 Linus Torvalds
*
* Modified for ARM by Russell King
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <asm/semaphore.h>
/*
* 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 semaphore spinlock.
*
* 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 <asm/semaphore.h>
* 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.
*/
void __up(struct semaphore *sem)
{
wake_up(&sem->wait);
}
static DEFINE_SPINLOCK(semaphore_lock);
void __sched __down(struct semaphore * sem)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
tsk->state = TASK_UNINTERRUPTIBLE;
add_wait_queue_exclusive(&sem->wait, &wait);
spin_lock_irq(&semaphore_lock);
sem->sleepers++;
for (;;) {
int sleepers = sem->sleepers;
/*
* Add "everybody else" into it. They aren't
* playing, because we own the spinlock.
*/
if (!atomic_add_negative(sleepers - 1, &sem->count)) {
sem->sleepers = 0;
break;
}
sem->sleepers = 1; /* us - see -1 above */
spin_unlock_irq(&semaphore_lock);
schedule();
tsk->state = TASK_UNINTERRUPTIBLE;
spin_lock_irq(&semaphore_lock);
}
spin_unlock_irq(&semaphore_lock);
remove_wait_queue(&sem->wait, &wait);
tsk->state = TASK_RUNNING;
wake_up(&sem->wait);
}
int __sched __down_interruptible(struct semaphore * sem)
{
int retval = 0;
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
tsk->state = TASK_INTERRUPTIBLE;
add_wait_queue_exclusive(&sem->wait, &wait);
spin_lock_irq(&semaphore_lock);
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. The
* "-1" is because we're still hoping to get
* the lock.
*/
if (!atomic_add_negative(sleepers - 1, &sem->count)) {
sem->sleepers = 0;
break;
}
sem->sleepers = 1; /* us - see -1 above */
spin_unlock_irq(&semaphore_lock);
schedule();
tsk->state = TASK_INTERRUPTIBLE;
spin_lock_irq(&semaphore_lock);
}
spin_unlock_irq(&semaphore_lock);
tsk->state = TASK_RUNNING;
remove_wait_queue(&sem->wait, &wait);
wake_up(&sem->wait);
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.
*/
int __down_trylock(struct semaphore * sem)
{
int sleepers;
unsigned long flags;
spin_lock_irqsave(&semaphore_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.
*/
if (!atomic_add_negative(sleepers, &sem->count))
wake_up(&sem->wait);
spin_unlock_irqrestore(&semaphore_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.
*
* ip contains the semaphore pointer on entry. Save the C-clobbered
* registers (r0 to r3 and lr), but not ip, as we use it as a return
* value in some cases..
* To remain AAPCS compliant (64-bit stack align) we save r4 as well.
*/
asm(" .section .sched.text,\"ax\",%progbits \n\
.align 5 \n\
.globl __down_failed \n\
__down_failed: \n\
stmfd sp!, {r0 - r4, lr} \n\
mov r0, ip \n\
bl __down \n\
ldmfd sp!, {r0 - r4, pc} \n\
\n\
.align 5 \n\
.globl __down_interruptible_failed \n\
__down_interruptible_failed: \n\
stmfd sp!, {r0 - r4, lr} \n\
mov r0, ip \n\
bl __down_interruptible \n\
mov ip, r0 \n\
ldmfd sp!, {r0 - r4, pc} \n\
\n\
.align 5 \n\
.globl __down_trylock_failed \n\
__down_trylock_failed: \n\
stmfd sp!, {r0 - r4, lr} \n\
mov r0, ip \n\
bl __down_trylock \n\
mov ip, r0 \n\
ldmfd sp!, {r0 - r4, pc} \n\
\n\
.align 5 \n\
.globl __up_wakeup \n\
__up_wakeup: \n\
stmfd sp!, {r0 - r4, lr} \n\
mov r0, ip \n\
bl __up \n\
ldmfd sp!, {r0 - r4, pc} \n\
");
EXPORT_SYMBOL(__down_failed);
EXPORT_SYMBOL(__down_interruptible_failed);
EXPORT_SYMBOL(__down_trylock_failed);
EXPORT_SYMBOL(__up_wakeup);
......@@ -6,7 +6,7 @@ extra-y := head.o vmlinux.lds
obj-$(CONFIG_SUBARCH_AVR32B) += entry-avr32b.o
obj-y += syscall_table.o syscall-stubs.o irq.o
obj-y += setup.o traps.o semaphore.o ocd.o ptrace.o
obj-y += setup.o traps.o ocd.o ptrace.o
obj-y += signal.o sys_avr32.o process.o time.o
obj-y += init_task.o switch_to.o cpu.o
obj-$(CONFIG_MODULES) += module.o avr32_ksyms.o
......
/*
* AVR32 sempahore implementation.
*
* Copyright (C) 2004-2006 Atmel Corporation
*
* Based on linux/arch/i386/kernel/semaphore.c
* Copyright (C) 1999 Linus Torvalds
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <asm/semaphore.h>
#include <asm/atomic.h>
/*
* 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 <asm/semaphore.h>
* 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.
*/
void __up(struct semaphore *sem)
{
wake_up(&sem->wait);
}
EXPORT_SYMBOL(__up);
void __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_return(sleepers - 1, &sem->count) >= 0) {
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;
}
EXPORT_SYMBOL(__down);
int __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
* the wait_queue_head.
*/
if (atomic_add_return(sleepers - 1, &sem->count) >= 0) {
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;
}
EXPORT_SYMBOL(__down_interruptible);
......@@ -31,10 +31,6 @@ config ZONE_DMA
bool
default y
config SEMAPHORE_SLEEPERS
bool
default y
config GENERIC_FIND_NEXT_BIT
bool
default y
......
......@@ -42,11 +42,6 @@ EXPORT_SYMBOL(ip_fast_csum);
EXPORT_SYMBOL(kernel_thread);
EXPORT_SYMBOL(__up);
EXPORT_SYMBOL(__down);
EXPORT_SYMBOL(__down_trylock);
EXPORT_SYMBOL(__down_interruptible);
EXPORT_SYMBOL(is_in_rom);
EXPORT_SYMBOL(bfin_return_from_exception);
......
......@@ -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
......
......@@ -9,7 +9,6 @@
#include <linux/string.h>
#include <linux/tty.h>
#include <asm/semaphore.h>
#include <asm/processor.h>
#include <asm/uaccess.h>
#include <asm/checksum.h>
......@@ -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);
......