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>

3 files changed, 1 insertions, 236 deletions

diff --git a/arch/xtensa/kernel/Makefile b/arch/xtensa/kernel/Makefile
index f582d6a..7419dbc 100644
--- a/arch/xtensa/kernel/Makefile
+++ b/arch/xtensa/kernel/Makefile
@@ -5,7 +5,7 @@
 extra-y := head.o vmlinux.lds
 
 
-obj-y := align.o entry.o irq.o coprocessor.o process.o ptrace.o semaphore.o  \
+obj-y := align.o entry.o irq.o coprocessor.o process.o ptrace.o \
 	 setup.o signal.o syscall.o time.o traps.o vectors.o platform.o  \
 	 pci-dma.o init_task.o io.o
 
diff --git a/arch/xtensa/kernel/semaphore.c b/arch/xtensa/kernel/semaphore.c
deleted file mode 100644
index 995c641..0000000
--- a/arch/xtensa/kernel/semaphore.c
+++ /dev/null
@@ -1,226 +0,0 @@
-/*
- * arch/xtensa/kernel/semaphore.c
- *
- * Generic semaphore code. Buyer beware. Do your own specific changes
- * in <asm/semaphore-helper.h>
- *
- * This file is subject to the terms and conditions of the GNU General Public
- * License.  See the file "COPYING" in the main directory of this archive
- * for more details.
- *
- * Copyright (C) 2001 - 2005 Tensilica Inc.
- *
- * Joe Taylor	<joe@tensilica.com, joetylr@yahoo.com>
- * Chris Zankel	<chris@zankel.net>
- * Marc Gauthier<marc@tensilica.com, marc@alumni.uwaterloo.ca>
- * Kevin Chea
- */
-
-#include <linux/sched.h>
-#include <linux/wait.h>
-#include <linux/init.h>
-#include <asm/semaphore.h>
-#include <asm/errno.h>
-
-/*
- * These two _must_ execute atomically wrt each other.
- */
-
-static __inline__ void wake_one_more(struct semaphore * sem)
-{
-	atomic_inc((atomic_t *)&sem->sleepers);
-}
-
-static __inline__ int waking_non_zero(struct semaphore *sem)
-{
-	unsigned long flags;
-	int ret = 0;
-
-	spin_lock_irqsave(&semaphore_wake_lock, flags);
-	if (sem->sleepers > 0) {
-		sem->sleepers--;
-		ret = 1;
-	}
-	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
-	return ret;
-}
-
-/*
- * waking_non_zero_interruptible:
- *	1	got the lock
- *	0	go to sleep
- *	-EINTR	interrupted
- *
- * We must undo the sem->count down_interruptible() increment while we are
- * protected by the spinlock in order to make atomic this atomic_inc() with the
- * atomic_read() in wake_one_more(), otherwise we can race. -arca
- */
-
-static __inline__ int waking_non_zero_interruptible(struct semaphore *sem,
-						struct task_struct *tsk)
-{
-	unsigned long flags;
-	int ret = 0;
-
-	spin_lock_irqsave(&semaphore_wake_lock, flags);
-	if (sem->sleepers > 0) {
-		sem->sleepers--;
-		ret = 1;
-	} else if (signal_pending(tsk)) {
-		atomic_inc(&sem->count);
-		ret = -EINTR;
-	}
-	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
-	return ret;
-}
-
-/*
- * waking_non_zero_trylock:
- *	1	failed to lock
- *	0	got the lock
- *
- * We must undo the sem->count down_trylock() increment while we are
- * protected by the spinlock in order to make atomic this atomic_inc() with the
- * atomic_read() in wake_one_more(), otherwise we can race. -arca
- */
-
-static __inline__ int waking_non_zero_trylock(struct semaphore *sem)
-{
-	unsigned long flags;
-	int ret = 1;
-
-	spin_lock_irqsave(&semaphore_wake_lock, flags);
-	if (sem->sleepers <= 0)
-		atomic_inc(&sem->count);
-	else {
-		sem->sleepers--;
-		ret = 0;
-	}
-	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
-	return ret;
-}
-
-DEFINE_SPINLOCK(semaphore_wake_lock);
-
-/*
- * Semaphores are implemented using a two-way counter:
- * The "count" variable is decremented for each process
- * that tries to sleep, while the "waking" variable is
- * incremented when the "up()" code goes to wake up waiting
- * processes.
- *
- * 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.
- *
- * waking_non_zero() (from asm/semaphore.h) must execute
- * atomically.
- *
- * When __up() is called, the count was negative before
- * incrementing it, and we need to wake up somebody.
- *
- * This routine adds one to the count of processes that need to
- * wake up and exit.  ALL waiting processes actually wake up but
- * only the one that gets to the "waking" field first will gate
- * through and acquire the semaphore.  The others will go back
- * to sleep.
- *
- * 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.
- */
-
-void __up(struct semaphore *sem)
-{
-	wake_one_more(sem);
-	wake_up(&sem->wait);
-}
-
-/*
- * 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()".
- *
- */
-
-#define DOWN_VAR				\
-	struct task_struct *tsk = current;	\
-	wait_queue_t wait;			\
-	init_waitqueue_entry(&wait, tsk);
-
-#define DOWN_HEAD(task_state)						\
-									\
-									\
-	tsk->state = (task_state);					\
-	add_wait_queue(&sem->wait, &wait);				\
-									\
-	/*								\
-	 * Ok, we're set up.  sem->count is known to be less than zero	\
-	 * so we must wait.						\
-	 *								\
-	 * We can let go the lock for purposes of waiting.		\
-	 * We re-acquire it after awaking so as to protect		\
-	 * all semaphore operations.					\
-	 *								\
-	 * If "up()" is called before we call waking_non_zero() then	\
-	 * we will catch it right away.  If it is called later then	\
-	 * we will have to go through a wakeup cycle to catch it.	\
-	 *								\
-	 * Multiple waiters contend for the semaphore lock to see	\
-	 * who gets to gate through and who has to wait some more.	\
-	 */								\
-	for (;;) {
-
-#define DOWN_TAIL(task_state)			\
-		tsk->state = (task_state);	\
-	}					\
-	tsk->state = TASK_RUNNING;		\
-	remove_wait_queue(&sem->wait, &wait);
-
-void __sched __down(struct semaphore * sem)
-{
-	DOWN_VAR
-	DOWN_HEAD(TASK_UNINTERRUPTIBLE)
-	if (waking_non_zero(sem))
-		break;
-	schedule();
-	DOWN_TAIL(TASK_UNINTERRUPTIBLE)
-}
-
-int __sched __down_interruptible(struct semaphore * sem)
-{
-	int ret = 0;
-	DOWN_VAR
-	DOWN_HEAD(TASK_INTERRUPTIBLE)
-
-	ret = waking_non_zero_interruptible(sem, tsk);
-	if (ret)
-	{
-		if (ret == 1)
-			/* ret != 0 only if we get interrupted -arca */
-			ret = 0;
-		break;
-	}
-	schedule();
-	DOWN_TAIL(TASK_INTERRUPTIBLE)
-	return ret;
-}
-
-int __down_trylock(struct semaphore * sem)
-{
-	return waking_non_zero_trylock(sem);
-}
diff --git a/arch/xtensa/kernel/xtensa_ksyms.c b/arch/xtensa/kernel/xtensa_ksyms.c
index 60dbdb4..6e52cdd 100644
--- a/arch/xtensa/kernel/xtensa_ksyms.c
+++ b/arch/xtensa/kernel/xtensa_ksyms.c
@@ -26,7 +26,6 @@
 #include <asm/io.h>
 #include <asm/page.h>
 #include <asm/pgalloc.h>
-#include <asm/semaphore.h>
 #ifdef CONFIG_BLK_DEV_FD
 #include <asm/floppy.h>
 #endif
@@ -71,14 +70,6 @@ EXPORT_SYMBOL(__umodsi3);
 EXPORT_SYMBOL(__udivdi3);
 EXPORT_SYMBOL(__umoddi3);
 
-/*
- * Semaphore operations
- */
-EXPORT_SYMBOL(__down);
-EXPORT_SYMBOL(__down_interruptible);
-EXPORT_SYMBOL(__down_trylock);
-EXPORT_SYMBOL(__up);
-
 #ifdef CONFIG_NET
 /*
  * Networking support