patch-2.4.2 linux/arch/cris/kernel/semaphore.c

• Lines: 239
• Date: Thu Feb 8 16:32:44 2001
• Orig file: v2.4.1/linux/arch/cris/kernel/semaphore.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.1/linux/arch/cris/kernel/semaphore.c linux/arch/cris/kernel/semaphore.c
@@ -0,0 +1,238 @@
+/*
+ *  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 __down(struct semaphore * sem)
+{
+	DOWN_VAR
+	DOWN_HEAD(TASK_UNINTERRUPTIBLE)
+	if (waking_non_zero(sem))
+		break;
+	schedule();
+	DOWN_TAIL(TASK_UNINTERRUPTIBLE)
+}
+
+int __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);
+}
+
+/*
+ * RW Semaphores
+ */
+void
+__down_read(struct rw_semaphore *sem, int count)
+{
+	DOWN_VAR;
+
+ retry_down:
+	if (count < 0) {
+		/* Wait for the lock to become unbiased.  Readers
+		   are non-exclusive.  */
+		
+		/* This takes care of granting the lock.  */
+		up_read(sem);
+
+		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;
+
+		mb();
+		count = atomic_dec_return(&sem->count);
+		if (count <= 0)
+			goto retry_down;
+	} else {
+		add_wait_queue(&sem->wait, &wait);
+
+		while (1) {
+			if (test_and_clear_bit(0, &sem->granted))
+				break;
+			set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+			if ((sem->granted & 1) == 0)
+				schedule();
+		}
+
+		remove_wait_queue(&sem->wait, &wait);
+		tsk->state = TASK_RUNNING;
+	}
+}
+
+void
+__down_write(struct rw_semaphore *sem, int count)
+{
+	DOWN_VAR;
+
+ retry_down:
+	if (count + RW_LOCK_BIAS < 0) {
+		up_write(sem);
+
+		add_wait_queue_exclusive(&sem->wait, &wait);
+	
+		while (atomic_read(&sem->count) < 0) {
+			set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+			if (atomic_read(&sem->count) >= RW_LOCK_BIAS)
+				break;
+			schedule();
+		}
+
+		remove_wait_queue(&sem->wait, &wait);
+		tsk->state = TASK_RUNNING;
+
+		mb();
+		count = atomic_sub_return(RW_LOCK_BIAS, &sem->count);
+		if (count != 0)
+			goto retry_down;
+	} else {
+		/* Put ourselves at the end of the list.  */
+		add_wait_queue_exclusive(&sem->write_bias_wait, &wait);
+
+		while (1) {
+			if (test_and_clear_bit(1, &sem->granted))
+				break;
+			set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+			if ((sem->granted & 2) == 0)
+				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);
+	}
+}
+
+void
+__rwsem_wake(struct rw_semaphore *sem, unsigned long readers)
+{
+	if (readers) {
+		if (test_and_set_bit(0, &sem->granted))
+			BUG();
+		wake_up(&sem->wait);
+	} else {
+		if (test_and_set_bit(1, &sem->granted))
+			BUG();
+		wake_up(&sem->write_bias_wait);
+	}
+}