patch-2.4.0-test12 linux/arch/parisc/kernel/semaphore.c

• Lines: 240
• Date: Tue Dec 5 12:29:39 2000
• Orig file: v2.4.0-test11/linux/arch/parisc/kernel/semaphore.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.0-test11/linux/arch/parisc/kernel/semaphore.c linux/arch/parisc/kernel/semaphore.c
@@ -0,0 +1,239 @@
+/*
+ * Just taken from alpha implementation.
+ * This can't work well, perhaps.
+ */
+/*
+ *  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_HEAD(task_state)						\
+									\
+									\
+	current->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)			\
+		current->state = (task_state);	\
+	}					\
+	current->state = TASK_RUNNING;		\
+	remove_wait_queue(&sem->wait, &wait);
+
+void __down(struct semaphore * sem)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	DOWN_HEAD(TASK_UNINTERRUPTIBLE)
+	if (waking_non_zero(sem))
+		break;
+	schedule();
+	DOWN_TAIL(TASK_UNINTERRUPTIBLE)
+}
+
+int __down_interruptible(struct semaphore * sem)
+{
+	DECLARE_WAITQUEUE(wait, current);
+	int ret = 0;
+
+	DOWN_HEAD(TASK_INTERRUPTIBLE)
+
+	ret = waking_non_zero_interruptible(sem, current);
+	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);
+}
+
+
+/* Wait for the lock to become unbiased.  Readers
+ * are non-exclusive. =)
+ */
+void down_read_failed(struct rw_semaphore *sem)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	__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(current, TASK_UNINTERRUPTIBLE);
+		if (atomic_read(&sem->count) >= 0)
+			break;
+		schedule();
+	}
+
+	remove_wait_queue(&sem->wait, &wait);
+	current->state = TASK_RUNNING;
+}
+
+void down_read_failed_biased(struct rw_semaphore *sem)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	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(current, TASK_UNINTERRUPTIBLE);
+                if (!sem->read_bias_granted)
+			schedule();
+	}
+
+	remove_wait_queue(&sem->wait, &wait);
+	current->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)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	__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(current, 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);
+	current->state = TASK_RUNNING;
+}
+
+void down_write_failed_biased(struct rw_semaphore *sem)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	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(current, TASK_UNINTERRUPTIBLE | TASK_EXCLUSIVE);
+		if (!sem->write_bias_granted)
+			schedule();
+	}
+
+	remove_wait_queue(&sem->write_bias_wait, &wait);
+	current->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);
+}
+
+
+/* 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_writer(struct rw_semaphore *sem)
+{
+	if (xchg(&sem->write_bias_granted, 1))
+		BUG();
+	wake_up(&sem->write_bias_wait);
+}