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, 191 deletions

diff --git a/arch/m32r/kernel/Makefile b/arch/m32r/kernel/Makefile
index e97e26e87c9e..09200d4886e3 100644
--- a/arch/m32r/kernel/Makefile
+++ b/arch/m32r/kernel/Makefile
@@ -5,7 +5,7 @@
 extra-y := head.o init_task.o vmlinux.lds
 
 obj-y   := process.o entry.o traps.o align.o irq.o setup.o time.o \
-        m32r_ksyms.o sys_m32r.o semaphore.o signal.o ptrace.o
+        m32r_ksyms.o sys_m32r.o signal.o ptrace.o
 
 obj-$(CONFIG_SMP)               += smp.o smpboot.o
 obj-$(CONFIG_MODULES)           += module.o
diff --git a/arch/m32r/kernel/m32r_ksyms.c b/arch/m32r/kernel/m32r_ksyms.c
index 41a4c95e06d6..e6709fe950ba 100644
--- a/arch/m32r/kernel/m32r_ksyms.c
+++ b/arch/m32r/kernel/m32r_ksyms.c
@@ -7,7 +7,6 @@
 #include <linux/interrupt.h>
 #include <linux/string.h>
 
-#include <asm/semaphore.h>
 #include <asm/processor.h>
 #include <asm/uaccess.h>
 #include <asm/checksum.h>
@@ -22,10 +21,6 @@ EXPORT_SYMBOL(dump_fpu);
 EXPORT_SYMBOL(__ioremap);
 EXPORT_SYMBOL(iounmap);
 EXPORT_SYMBOL(kernel_thread);
-EXPORT_SYMBOL(__down);
-EXPORT_SYMBOL(__down_interruptible);
-EXPORT_SYMBOL(__up);
-EXPORT_SYMBOL(__down_trylock);
 
 /* Networking helper routines. */
 /* Delay loops */
diff --git a/arch/m32r/kernel/semaphore.c b/arch/m32r/kernel/semaphore.c
deleted file mode 100644
index 940c2d37cfd1..000000000000
--- a/arch/m32r/kernel/semaphore.c
+++ /dev/null
@@ -1,185 +0,0 @@
-/*
- *  linux/arch/m32r/semaphore.c
- *    orig : i386 2.6.4
- *
- *  M32R semaphore implementation.
- *
- *      Copyright (c) 2002 - 2004 Hitoshi Yamamoto
- */
-
-/*
- * i386 semaphore implementation.
- *
- * (C) Copyright 1999 Linus Torvalds
- *
- * Portions Copyright 1999 Red Hat, Inc.
- *
- *      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.
- *
- * rw semaphores implemented November 1999 by Benjamin LaHaise <bcrl@kvack.org>
- */
-#include <linux/sched.h>
-#include <linux/err.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 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.
- */
-
-/*
- * 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.
- */
-
-asmlinkage void __up(struct semaphore *sem)
-{
-        wake_up(&sem->wait);
-}
-
-asmlinkage 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;
-}
-
-asmlinkage 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.
- *
- * We could have done the trylock with a
- * single "cmpxchg" without failure cases,
- * but then it wouldn't work on a 386.
- */
-asmlinkage int __down_trylock(struct semaphore * sem)
-{
-        int sleepers;
-        unsigned long flags;
-
-        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;
-}