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>

2 files changed, 1 insertions, 222 deletions

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 00d44c6fbfe..6235f72a14f 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -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
diff --git a/arch/arm/kernel/semaphore.c b/arch/arm/kernel/semaphore.c
deleted file mode 100644
index 981fe5c6ccb..00000000000
--- a/arch/arm/kernel/semaphore.c
+++ /dev/null
@@ -1,221 +0,0 @@
-/*
- *  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);