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, 169 deletions

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 9e78e1a4ca17..6fcdb6fda2e2 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -5,7 +5,7 @@
 extra-y		:= head.o init_task.o vmlinux.lds
 
 obj-y		+= cpu-probe.o branch.o entry.o genex.o irq.o process.o \
-		   ptrace.o reset.o semaphore.o setup.o signal.o syscall.o \
+		   ptrace.o reset.o setup.o signal.o syscall.o \
 		   time.o topology.o traps.o unaligned.o
 
 obj-$(CONFIG_CEVT_BCM1480)	+= cevt-bcm1480.o
diff --git a/arch/mips/kernel/semaphore.c b/arch/mips/kernel/semaphore.c
deleted file mode 100644
index 1265358cdca1..000000000000
--- a/arch/mips/kernel/semaphore.c
+++ /dev/null
@@ -1,168 +0,0 @@
-/*
- * MIPS-specific semaphore code.
- *
- * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
- * Copyright (C) 2004 Ralf Baechle <ralf@linux-mips.org>
- *
- * 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/module.h>
-#include <linux/sched.h>
-#include <linux/init.h>
-#include <asm/atomic.h>
-#include <asm/cpu-features.h>
-#include <asm/errno.h>
-#include <asm/semaphore.h>
-#include <asm/war.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;
- *
- * On machines without lld/scd we need a spinlock to make the manipulation of
- * sem->count and sem->waking atomic.  Scalability isn't an issue because
- * this lock is used on UP only so it's just an empty variable.
- */
-static inline int __sem_update_count(struct semaphore *sem, int incr)
-{
-	int old_count, tmp;
-
-	if (cpu_has_llsc && R10000_LLSC_WAR) {
-		__asm__ __volatile__(
-		"	.set	mips3					\n"
-		"1:	ll	%0, %2		# __sem_update_count	\n"
-		"	sra	%1, %0, 31				\n"
-		"	not	%1					\n"
-		"	and	%1, %0, %1				\n"
-		"	addu	%1, %1, %3				\n"
-		"	sc	%1, %2					\n"
-		"	beqzl	%1, 1b					\n"
-		"	.set	mips0					\n"
-		: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
-		: "r" (incr), "m" (sem->count));
-	} else if (cpu_has_llsc) {
-		__asm__ __volatile__(
-		"	.set	mips3					\n"
-		"1:	ll	%0, %2		# __sem_update_count	\n"
-		"	sra	%1, %0, 31				\n"
-		"	not	%1					\n"
-		"	and	%1, %0, %1				\n"
-		"	addu	%1, %1, %3				\n"
-		"	sc	%1, %2					\n"
-		"	beqz	%1, 1b					\n"
-		"	.set	mips0					\n"
-		: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
-		: "r" (incr), "m" (sem->count));
-	} else {
-		static DEFINE_SPINLOCK(semaphore_lock);
-		unsigned long flags;
-
-		spin_lock_irqsave(&semaphore_lock, flags);
-		old_count = atomic_read(&sem->count);
-		tmp = max_t(int, old_count, 0) + incr;
-		atomic_set(&sem->count, tmp);
-		spin_unlock_irqrestore(&semaphore_lock, flags);
-	}
-
-	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);