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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/cris/kernel
parente48b3deee475134585eed03e7afebe4bf9e0dba9 (diff)
downloadvexpress-lsk-64ac24e738823161693bf791f87adc802cf529ff.tar.gz
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/cris/kernel')
-rw-r--r--arch/cris/kernel/Makefile3
-rw-r--r--arch/cris/kernel/crisksyms.c7
-rw-r--r--arch/cris/kernel/semaphore.c129
3 files changed, 1 insertions, 138 deletions
diff --git a/arch/cris/kernel/Makefile b/arch/cris/kernel/Makefile
index c8e8ea57098..ee7bcd4d20b 100644
--- a/arch/cris/kernel/Makefile
+++ b/arch/cris/kernel/Makefile
@@ -5,8 +5,7 @@
extra-y := vmlinux.lds
-obj-y := process.o traps.o irq.o ptrace.o setup.o \
- time.o sys_cris.o semaphore.o
+obj-y := process.o traps.o irq.o ptrace.o setup.o time.o sys_cris.o
obj-$(CONFIG_MODULES) += crisksyms.o
obj-$(CONFIG_MODULES) += module.o
diff --git a/arch/cris/kernel/crisksyms.c b/arch/cris/kernel/crisksyms.c
index 62f0e752915..7ac000f6a88 100644
--- a/arch/cris/kernel/crisksyms.c
+++ b/arch/cris/kernel/crisksyms.c
@@ -9,7 +9,6 @@
#include <linux/string.h>
#include <linux/tty.h>
-#include <asm/semaphore.h>
#include <asm/processor.h>
#include <asm/uaccess.h>
#include <asm/checksum.h>
@@ -49,12 +48,6 @@ EXPORT_SYMBOL(__negdi2);
EXPORT_SYMBOL(__ioremap);
EXPORT_SYMBOL(iounmap);
-/* Semaphore functions */
-EXPORT_SYMBOL(__up);
-EXPORT_SYMBOL(__down);
-EXPORT_SYMBOL(__down_interruptible);
-EXPORT_SYMBOL(__down_trylock);
-
/* Userspace access functions */
EXPORT_SYMBOL(__copy_user_zeroing);
EXPORT_SYMBOL(__copy_user);
diff --git a/arch/cris/kernel/semaphore.c b/arch/cris/kernel/semaphore.c
deleted file mode 100644
index f137a439041..00000000000
--- a/arch/cris/kernel/semaphore.c
+++ /dev/null
@@ -1,129 +0,0 @@
-/*
- * Generic semaphore code. Buyer beware. Do your own
- * specific changes in <asm/semaphore-helper.h>
- */
-
-#include <linux/sched.h>
-#include <asm/semaphore-helper.h>
-
-/*
- * 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);
-}