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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/ia64/kernel/semaphore.c
downloadlinux-stericsson-2.6.12-rc2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'arch/ia64/kernel/semaphore.c')
-rw-r--r--arch/ia64/kernel/semaphore.c165
1 files changed, 165 insertions, 0 deletions
diff --git a/arch/ia64/kernel/semaphore.c b/arch/ia64/kernel/semaphore.c
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+++ b/arch/ia64/kernel/semaphore.c
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+/*
+ * 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;
+}