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, 172 deletions

diff --git a/arch/ia64/kernel/Makefile b/arch/ia64/kernel/Makefile
index 33e5a598672d..13fd10e8699e 100644
--- a/arch/ia64/kernel/Makefile
+++ b/arch/ia64/kernel/Makefile
@@ -6,7 +6,7 @@ extra-y	:= head.o init_task.o vmlinux.lds
 
 obj-y := acpi.o entry.o efi.o efi_stub.o gate-data.o fsys.o ia64_ksyms.o irq.o irq_ia64.o       \
          irq_lsapic.o ivt.o machvec.o pal.o patch.o process.o perfmon.o ptrace.o sal.o          \
-         salinfo.o semaphore.o setup.o signal.o sys_ia64.o time.o traps.o unaligned.o \
+         salinfo.o setup.o signal.o sys_ia64.o time.o traps.o unaligned.o \
          unwind.o mca.o mca_asm.o topology.o
 
 obj-$(CONFIG_IA64_BRL_EMU)      += brl_emu.o
diff --git a/arch/ia64/kernel/ia64_ksyms.c b/arch/ia64/kernel/ia64_ksyms.c
index 8e7193d55528..6da1f20d7372 100644
--- a/arch/ia64/kernel/ia64_ksyms.c
+++ b/arch/ia64/kernel/ia64_ksyms.c
@@ -19,12 +19,6 @@ EXPORT_SYMBOL_GPL(empty_zero_page);
 EXPORT_SYMBOL(ip_fast_csum);            /* hand-coded assembly */
 EXPORT_SYMBOL(csum_ipv6_magic);
 
-#include <asm/semaphore.h>
-EXPORT_SYMBOL(__down);
-EXPORT_SYMBOL(__down_interruptible);
-EXPORT_SYMBOL(__down_trylock);
-EXPORT_SYMBOL(__up);
-
 #include <asm/page.h>
 EXPORT_SYMBOL(clear_page);
 
diff --git a/arch/ia64/kernel/semaphore.c b/arch/ia64/kernel/semaphore.c
deleted file mode 100644
index 2724ef3fbae2..000000000000
--- a/arch/ia64/kernel/semaphore.c
+++ /dev/null
@@ -1,165 +0,0 @@
-/*
- * IA-64 semaphore implementation (derived from x86 version).
- *
- * Copyright (C) 1999-2000, 2002 Hewlett-Packard Co
- *      David Mosberger-Tang <davidm@hpl.hp.com>
- */
-
-/*
- * Semaphores are implemented using a two-way counter: The "count"
- * variable is decremented for each process that tries to acquire the
- * semaphore, while the "sleepers" 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.
- */
-#include <linux/sched.h>
-#include <linux/init.h>
-
-#include <asm/errno.h>
-#include <asm/semaphore.h>
-
-/*
- * 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 "sleepers" 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);
-}
-
-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;
-}
-
-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.
- */
-int
-__down_trylock (struct semaphore *sem)
-{
-        unsigned long flags;
-        int sleepers;
-
-        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;
-}