From 64ac24e738823161693bf791f87adc802cf529ff Mon Sep 17 00:00:00 2001
From: Matthew Wilcox <matthew@wil.cx>
Date: Fri, 7 Mar 2008 21:55:58 -0500
Subject: 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: Matthew Wilcox <willy@linux.intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
---
arch/ia64/kernel/Makefile | 2 +-
arch/ia64/kernel/ia64_ksyms.c | 6 --
arch/ia64/kernel/semaphore.c | 165 ------------------------------------------
3 files changed, 1 insertion(+), 172 deletions(-)
delete mode 100644 arch/ia64/kernel/semaphore.c
(limited to 'arch/ia64/kernel')
diff --git a/arch/ia64/kernel/Makefile b/arch/ia64/kernel/Makefile
index 33e5a598672..13fd10e8699 100644
--- a/arch/ia64/kernel/Makefile
+++ b/arch/ia64/kernel/Makefile
@@ -6,7 +6,7 @@ extra-y := head.o init_task.o vmlinux.lds
obj-y := acpi.o entry.o efi.o efi_stub.o gate-data.o fsys.o ia64_ksyms.o irq.o irq_ia64.o \
irq_lsapic.o ivt.o machvec.o pal.o patch.o process.o perfmon.o ptrace.o sal.o \
- salinfo.o semaphore.o setup.o signal.o sys_ia64.o time.o traps.o unaligned.o \
+ salinfo.o setup.o signal.o sys_ia64.o time.o traps.o unaligned.o \
unwind.o mca.o mca_asm.o topology.o
obj-$(CONFIG_IA64_BRL_EMU) += brl_emu.o
diff --git a/arch/ia64/kernel/ia64_ksyms.c b/arch/ia64/kernel/ia64_ksyms.c
index 8e7193d5552..6da1f20d737 100644
--- a/arch/ia64/kernel/ia64_ksyms.c
+++ b/arch/ia64/kernel/ia64_ksyms.c
@@ -19,12 +19,6 @@ EXPORT_SYMBOL_GPL(empty_zero_page);
EXPORT_SYMBOL(ip_fast_csum); /* hand-coded assembly */
EXPORT_SYMBOL(csum_ipv6_magic);
-#include <asm/semaphore.h>
-EXPORT_SYMBOL(__down);
-EXPORT_SYMBOL(__down_interruptible);
-EXPORT_SYMBOL(__down_trylock);
-EXPORT_SYMBOL(__up);
-
#include <asm/page.h>
EXPORT_SYMBOL(clear_page);
diff --git a/arch/ia64/kernel/semaphore.c b/arch/ia64/kernel/semaphore.c
deleted file mode 100644
index 2724ef3fbae..00000000000
--- a/arch/ia64/kernel/semaphore.c
+++ /dev/null
@@ -1,165 +0,0 @@
-/*
- * IA-64 semaphore implementation (derived from x86 version).
- *
- * Copyright (C) 1999-2000, 2002 Hewlett-Packard Co
- * David Mosberger-Tang <davidm@hpl.hp.com>
- */
-
-/*
- * Semaphores are implemented using a two-way counter: The "count"
- * variable is decremented for each process that tries to acquire the
- * semaphore, while the "sleepers" 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.
- */
-#include <linux/sched.h>
-#include <linux/init.h>
-
-#include <asm/errno.h>
-#include <asm/semaphore.h>
-
-/*
- * 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 "sleepers" 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);
-}
-
-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_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;
-}
-
-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
- * 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.
- */
-int
-__down_trylock (struct semaphore *sem)
-{
- unsigned long flags;
- int sleepers;
-
- 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;
-}
--
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