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authorMatthew Wilcox <matthew@wil.cx>2008-03-07 21:55:58 -0500
committerMatthew Wilcox <willy@linux.intel.com>2008-04-17 10:42:34 -0400
commit64ac24e738823161693bf791f87adc802cf529ff (patch)
tree19c0b0cf314d4394ca580c05b86cdf874ce0a167 /arch/alpha
parente48b3deee475134585eed03e7afebe4bf9e0dba9 (diff)
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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>
Diffstat (limited to 'arch/alpha')
-rw-r--r--arch/alpha/kernel/Makefile2
-rw-r--r--arch/alpha/kernel/alpha_ksyms.c9
-rw-r--r--arch/alpha/kernel/semaphore.c224
3 files changed, 1 insertions, 234 deletions
diff --git a/arch/alpha/kernel/Makefile b/arch/alpha/kernel/Makefile
index dccf05245d4..ac706c1d7ad 100644
--- a/arch/alpha/kernel/Makefile
+++ b/arch/alpha/kernel/Makefile
@@ -7,7 +7,7 @@ EXTRA_AFLAGS := $(KBUILD_CFLAGS)
EXTRA_CFLAGS := -Werror -Wno-sign-compare
obj-y := entry.o traps.o process.o init_task.o osf_sys.o irq.o \
- irq_alpha.o signal.o setup.o ptrace.o time.o semaphore.o \
+ irq_alpha.o signal.o setup.o ptrace.o time.o \
alpha_ksyms.o systbls.o err_common.o io.o
obj-$(CONFIG_VGA_HOSE) += console.o
diff --git a/arch/alpha/kernel/alpha_ksyms.c b/arch/alpha/kernel/alpha_ksyms.c
index e9762a33b04..d96e742d4dc 100644
--- a/arch/alpha/kernel/alpha_ksyms.c
+++ b/arch/alpha/kernel/alpha_ksyms.c
@@ -77,15 +77,6 @@ EXPORT_SYMBOL(__do_clear_user);
EXPORT_SYMBOL(__strncpy_from_user);
EXPORT_SYMBOL(__strnlen_user);
-/* Semaphore helper functions. */
-EXPORT_SYMBOL(__down_failed);
-EXPORT_SYMBOL(__down_failed_interruptible);
-EXPORT_SYMBOL(__up_wakeup);
-EXPORT_SYMBOL(down);
-EXPORT_SYMBOL(down_interruptible);
-EXPORT_SYMBOL(down_trylock);
-EXPORT_SYMBOL(up);
-
/*
* SMP-specific symbols.
*/
diff --git a/arch/alpha/kernel/semaphore.c b/arch/alpha/kernel/semaphore.c
deleted file mode 100644
index 8d2982aa1b8..00000000000
--- a/arch/alpha/kernel/semaphore.c
+++ /dev/null
@@ -1,224 +0,0 @@
-/*
- * Alpha semaphore implementation.
- *
- * (C) Copyright 1996 Linus Torvalds
- * (C) Copyright 1999, 2000 Richard Henderson
- */
-
-#include <linux/errno.h>
-#include <linux/sched.h>
-#include <linux/init.h>
-
-/*
- * This is basically the PPC semaphore scheme ported to use
- * the Alpha ll/sc sequences, so see the PPC code for
- * credits.
- */
-
-/*
- * 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;
- */
-static inline int __sem_update_count(struct semaphore *sem, int incr)
-{
- long old_count, tmp = 0;
-
- __asm__ __volatile__(
- "1: ldl_l %0,%2\n"
- " cmovgt %0,%0,%1\n"
- " addl %1,%3,%1\n"
- " stl_c %1,%2\n"
- " beq %1,2f\n"
- " mb\n"
- ".subsection 2\n"
- "2: br 1b\n"
- ".previous"
- : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
- : "Ir" (incr), "1" (tmp), "m" (sem->count));
-
- return old_count;
-}
-
-/*
- * 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()".
- */
-
-void __sched
-__down_failed(struct semaphore *sem)
-{
- struct task_struct *tsk = current;
- DECLARE_WAITQUEUE(wait, tsk);
-
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): down failed(%p)\n",
- tsk->comm, task_pid_nr(tsk), sem);
-#endif
-
- tsk->state = TASK_UNINTERRUPTIBLE;
- wmb();
- 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);
- tsk->state = 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);
-
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): down acquired(%p)\n",
- tsk->comm, task_pid_nr(tsk), sem);
-#endif
-}
-
-int __sched
-__down_failed_interruptible(struct semaphore *sem)
-{
- struct task_struct *tsk = current;
- DECLARE_WAITQUEUE(wait, tsk);
- long ret = 0;
-
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): down failed(%p)\n",
- tsk->comm, task_pid_nr(tsk), sem);
-#endif
-
- tsk->state = TASK_INTERRUPTIBLE;
- wmb();
- 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);
- ret = -EINTR;
- break;
- }
- schedule();
- set_task_state(tsk, TASK_INTERRUPTIBLE);
- }
-
- remove_wait_queue(&sem->wait, &wait);
- tsk->state = TASK_RUNNING;
- wake_up(&sem->wait);
-
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): down %s(%p)\n",
- current->comm, task_pid_nr(current),
- (ret < 0 ? "interrupted" : "acquired"), sem);
-#endif
- return ret;
-}
-
-void
-__up_wakeup(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);
-}
-
-void __sched
-down(struct semaphore *sem)
-{
-#ifdef WAITQUEUE_DEBUG
- CHECK_MAGIC(sem->__magic);
-#endif
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): down(%p) <count=%d> from %p\n",
- current->comm, task_pid_nr(current), sem,
- atomic_read(&sem->count), __builtin_return_address(0));
-#endif
- __down(sem);
-}
-
-int __sched
-down_interruptible(struct semaphore *sem)
-{
-#ifdef WAITQUEUE_DEBUG
- CHECK_MAGIC(sem->__magic);
-#endif
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): down(%p) <count=%d> from %p\n",
- current->comm, task_pid_nr(current), sem,
- atomic_read(&sem->count), __builtin_return_address(0));
-#endif
- return __down_interruptible(sem);
-}
-
-int
-down_trylock(struct semaphore *sem)
-{
- int ret;
-
-#ifdef WAITQUEUE_DEBUG
- CHECK_MAGIC(sem->__magic);
-#endif
-
- ret = __down_trylock(sem);
-
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): down_trylock %s from %p\n",
- current->comm, task_pid_nr(current),
- ret ? "failed" : "acquired",
- __builtin_return_address(0));
-#endif
-
- return ret;
-}
-
-void
-up(struct semaphore *sem)
-{
-#ifdef WAITQUEUE_DEBUG
- CHECK_MAGIC(sem->__magic);
-#endif
-#ifdef CONFIG_DEBUG_SEMAPHORE
- printk("%s(%d): up(%p) <count=%d> from %p\n",
- current->comm, task_pid_nr(current), sem,
- atomic_read(&sem->count), __builtin_return_address(0));
-#endif
- __up(sem);
-}