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, 174 deletions

diff --git a/arch/v850/kernel/Makefile b/arch/v850/kernel/Makefile
index 3930482bddc4..da5889c53576 100644
--- a/arch/v850/kernel/Makefile
+++ b/arch/v850/kernel/Makefile
@@ -11,7 +11,7 @@
 
 extra-y := head.o init_task.o vmlinux.lds
 
-obj-y += intv.o entry.o process.o syscalls.o time.o semaphore.o setup.o \
+obj-y += intv.o entry.o process.o syscalls.o time.o setup.o \
          signal.o irq.o mach.o ptrace.o bug.o
 obj-$(CONFIG_MODULES)           += module.o v850_ksyms.o
 # chip-specific code
diff --git a/arch/v850/kernel/semaphore.c b/arch/v850/kernel/semaphore.c
deleted file mode 100644
index fc89fd661c99..000000000000
--- a/arch/v850/kernel/semaphore.c
+++ /dev/null
@@ -1,166 +0,0 @@
-/*
- * arch/v850/kernel/semaphore.c -- Semaphore support
- *
- *  Copyright (C) 1998-2000  IBM Corporation
- *  Copyright (C) 1999  Linus Torvalds
- *
- * 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.
- *
- * This file is a copy of the s390 version, arch/s390/kernel/semaphore.c
- *    Author(s): Martin Schwidefsky
- * which was derived from the i386 version, linux/arch/i386/kernel/semaphore.c
- */
-
-#include <linux/errno.h>
-#include <linux/sched.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.
- */
-int __down_trylock(struct semaphore * sem)
-{
-        unsigned long flags;
-        int sleepers;
-
-        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;
-}
diff --git a/arch/v850/kernel/v850_ksyms.c b/arch/v850/kernel/v850_ksyms.c
index 93575fdc874d..8d386a5dbc4a 100644
--- a/arch/v850/kernel/v850_ksyms.c
+++ b/arch/v850/kernel/v850_ksyms.c
@@ -11,7 +11,6 @@
 #include <asm/pgalloc.h>
 #include <asm/irq.h>
 #include <asm/io.h>
-#include <asm/semaphore.h>
 #include <asm/checksum.h>
 #include <asm/current.h>
 
@@ -34,12 +33,6 @@ EXPORT_SYMBOL (memset);
 EXPORT_SYMBOL (memcpy);
 EXPORT_SYMBOL (memmove);
 
-/* semaphores */
-EXPORT_SYMBOL (__down);
-EXPORT_SYMBOL (__down_interruptible);
-EXPORT_SYMBOL (__down_trylock);
-EXPORT_SYMBOL (__up);
-
 /*
  * libgcc functions - functions that are used internally by the
  * compiler...  (prototypes are not correct though, but that