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Generic semaphore implementation

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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 <willy@linux.intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Matthew Wilcox
2008-03-07 21:55:58 -05:00
committed by Matthew Wilcox
parent e48b3deee4
commit 64ac24e738
113 changed files with 314 additions and 7679 deletions
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2
arch/powerpc/kernel/Makefile
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@@ -12,7 +12,7 @@ CFLAGS_prom_init.o += -fPIC
CFLAGS_btext.o += -fPIC
endif
obj-y := semaphore.o cputable.o ptrace.o syscalls.o \
obj-y := cputable.o ptrace.o syscalls.o \
irq.o align.o signal_32.o pmc.o vdso.o \
init_task.o process.o systbl.o idle.o \
signal.o

1
arch/powerpc/kernel/ppc_ksyms.c
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@@ -15,7 +15,6 @@
#include <linux/bitops.h>
#include <asm/page.h>
#include <asm/semaphore.h>
#include <asm/processor.h>
#include <asm/cacheflush.h>
#include <asm/uaccess.h>

135
arch/powerpc/kernel/semaphore.c
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@@ -1,135 +0,0 @@
/*
* PowerPC-specific semaphore code.
*
* Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
*
* 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.
*
* April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
* to eliminate the SMP races in the old version between the updates
* of `count' and `waking'. Now we use negative `count' values to
* indicate that some process(es) are waiting for the semaphore.
*/
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/module.h>
#include <asm/atomic.h>
#include <asm/semaphore.h>
#include <asm/errno.h>
/*
* 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)
{
int old_count, tmp;
__asm__ __volatile__("\n"
"1: lwarx %0,0,%3\n"
" srawi %1,%0,31\n"
" andc %1,%0,%1\n"
" add %1,%1,%4\n"
PPC405_ERR77(0,%3)
" stwcx. %1,0,%3\n"
" bne 1b"
: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
: "r" (&sem->count), "r" (incr), "m" (sem->count)
: "cc");
return old_count;
}
void __up(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);
}
EXPORT_SYMBOL(__up);
/*
* Note that when we come in to __down or __down_interruptible,
* we have already decremented count, but that decrement was
* ineffective since the result was < 0, and any negative value
* of count is equivalent to 0.
* Thus it is only when we decrement count from some value > 0
* that we have actually got the semaphore.
*/
void __sched __down(struct semaphore *sem)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
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);
__set_task_state(tsk, 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);
}
EXPORT_SYMBOL(__down);
int __sched __down_interruptible(struct semaphore * sem)
{
int retval = 0;
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
__set_task_state(tsk, TASK_INTERRUPTIBLE);
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);
retval = -EINTR;
break;
}
schedule();
set_task_state(tsk, TASK_INTERRUPTIBLE);
}
remove_wait_queue(&sem->wait, &wait);
__set_task_state(tsk, TASK_RUNNING);
wake_up(&sem->wait);
return retval;
}
EXPORT_SYMBOL(__down_interruptible);