patch-2.3.99-pre8 linux/arch/s390/kernel/semaphore.c

• Lines: 303
• Date: Fri May 12 11:41:45 2000
• Orig file: v2.3.99-pre7/linux/arch/s390/kernel/semaphore.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.3.99-pre7/linux/arch/s390/kernel/semaphore.c linux/arch/s390/kernel/semaphore.c
@@ -0,0 +1,302 @@
+/*
+ *  linux/arch/S390/kernel/semaphore.c
+ *
+ *  S390 version
+ *    Copyright (C) 1998 IBM Corporation
+ *    Author(s): Martin Schwidefsky
+ *
+ *  Derived from "linux/arch/i386/kernel/semaphore.c
+ *    Copyright (C) 1999, Linus Torvalds
+ *
+ */
+#include <linux/sched.h>
+
+#include <asm/semaphore.h>
+
+/*
+ * Semaphores are implemented using a two-way counter:
+ * The "count" variable is decremented for each process
+ * that tries to aquire the semaphore, while the "sleeping"
+ * variable is a count of such aquires.
+ *
+ * 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 spinlock_t semaphore_lock = SPIN_LOCK_UNLOCKED;
+
+void __down(struct semaphore * sem)
+{
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+	tsk->state = TASK_UNINTERRUPTIBLE|TASK_EXCLUSIVE;
+	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|TASK_EXCLUSIVE;
+		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 __down_interruptible(struct semaphore * sem)
+{
+	int retval = 0;
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+	tsk->state = TASK_INTERRUPTIBLE|TASK_EXCLUSIVE;
+	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|TASK_EXCLUSIVE;
+		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;
+}
+
+void down_read_failed_biased(struct rw_semaphore *sem)
+{
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+
+	add_wait_queue(&sem->wait, &wait);	/* put ourselves at the head of the list */
+
+	for (;;) {
+		if (sem->read_bias_granted && xchg(&sem->read_bias_granted, 0))
+			break;
+		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+		if (!sem->read_bias_granted)
+			schedule();
+	}
+
+	remove_wait_queue(&sem->wait, &wait);
+	tsk->state = TASK_RUNNING;
+}
+
+void down_write_failed_biased(struct rw_semaphore *sem)
+{
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+
+	add_wait_queue_exclusive(&sem->write_bias_wait, &wait);	/* put ourselves at the end of the list */
+
+	for (;;) {
+		if (sem->write_bias_granted && xchg(&sem->write_bias_granted, 0))
+			break;
+		set_task_state(tsk, TASK_UNINTERRUPTIBLE | TASK_EXCLUSIVE);
+		if (!sem->write_bias_granted)
+			schedule();
+	}
+
+	remove_wait_queue(&sem->write_bias_wait, &wait);
+	tsk->state = TASK_RUNNING;
+
+	/* if the lock is currently unbiased, awaken the sleepers
+	 * FIXME: this wakes up the readers early in a bit of a
+	 * stampede -> bad!
+	 */
+	if (atomic_read(&sem->count) >= 0)
+		wake_up(&sem->wait);
+}
+
+/* Wait for the lock to become unbiased.  Readers
+ * are non-exclusive. =)
+ */
+void down_read_failed(struct rw_semaphore *sem)
+{
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+
+	up_read(sem);	/* this takes care of granting the lock */
+
+	add_wait_queue(&sem->wait, &wait);
+
+	while (atomic_read(&sem->count) < 0) {
+		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+		if (atomic_read(&sem->count) >= 0)
+			break;
+		schedule();
+	}
+
+	remove_wait_queue(&sem->wait, &wait);
+	tsk->state = TASK_RUNNING;
+}
+
+/* Wait for the lock to become unbiased. Since we're
+ * a writer, we'll make ourselves exclusive.
+ */
+void down_write_failed(struct rw_semaphore *sem)
+{
+	struct task_struct *tsk = current;
+	DECLARE_WAITQUEUE(wait, tsk);
+
+	up_write(sem);	/* this takes care of granting the lock */
+
+	add_wait_queue_exclusive(&sem->wait, &wait);
+
+	while (atomic_read(&sem->count) < 0) {
+		set_task_state(tsk, TASK_UNINTERRUPTIBLE | TASK_EXCLUSIVE);
+		if (atomic_read(&sem->count) >= 0)
+			break;	/* we must attempt to aquire or bias the lock */
+		schedule();
+	}
+
+	remove_wait_queue(&sem->wait, &wait);
+	tsk->state = TASK_RUNNING;
+}
+
+/* Called when someone has done an up that transitioned from
+ * negative to non-negative, meaning that the lock has been
+ * granted to whomever owned the bias.
+ */
+void rwsem_wake_readers(struct rw_semaphore *sem)
+{
+	if (xchg(&sem->read_bias_granted, 1))
+		BUG();
+	wake_up(&sem->wait);
+}
+
+void rwsem_wake_writers(struct rw_semaphore *sem)
+{
+	if (xchg(&sem->write_bias_granted, 1))
+		BUG();
+	wake_up(&sem->write_bias_wait);
+}
+
+void __down_read_failed(int count, struct rw_semaphore *sem) 
+{
+	do {
+		if (count == -1) {
+			down_read_failed_biased(sem);
+			break;
+		}
+		down_read_failed(sem);
+		count = atomic_dec_return(&sem->count);
+	} while (count != 0);
+}
+
+void __down_write_failed(int count, struct rw_semaphore *sem)
+{
+	do {
+		if (count < 0 && count > -RW_LOCK_BIAS) {
+			down_write_failed_biased(sem);
+			break;
+		}
+		down_write_failed(sem);
+		count = atomic_add_return(-RW_LOCK_BIAS, &sem->count);
+	} while (count != 0);
+}
+
+void __rwsem_wake(int count, struct rw_semaphore *sem)
+{
+	if (count == 0)
+		rwsem_wake_readers(sem);
+	else
+		rwsem_wake_writers(sem);
+}
+