1 files changed, 344 insertions, 0 deletions
diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
new file mode 100644
index 00000000000..21f0db2c971
--- /dev/null
+++ b/lib/rwsem-spinlock.c
@@ -0,0 +1,344 @@
+/* rwsem-spinlock.c: R/W semaphores: contention handling functions for
+ * generic spinlock implementation
+ *
+ * Copyright (c) 2001   David Howells (dhowells@redhat.com).
+ * - Derived partially from idea by Andrea Arcangeli <andrea@suse.de>
+ * - Derived also from comments by Linus
+ */
+#include <linux/rwsem.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+
+struct rwsem_waiter {
+	struct list_head list;
+	struct task_struct *task;
+	unsigned int flags;
+#define RWSEM_WAITING_FOR_READ	0x00000001
+#define RWSEM_WAITING_FOR_WRITE	0x00000002
+};
+
+#if RWSEM_DEBUG
+void rwsemtrace(struct rw_semaphore *sem, const char *str)
+{
+	if (sem->debug)
+		printk("[%d] %s({%d,%d})\n",
+		       current->pid, str, sem->activity,
+		       list_empty(&sem->wait_list) ? 0 : 1);
+}
+#endif
+
+/*
+ * initialise the semaphore
+ */
+void fastcall init_rwsem(struct rw_semaphore *sem)
+{
+	sem->activity = 0;
+	spin_lock_init(&sem->wait_lock);
+	INIT_LIST_HEAD(&sem->wait_list);
+#if RWSEM_DEBUG
+	sem->debug = 0;
+#endif
+}
+
+/*
+ * handle the lock release when processes blocked on it that can now run
+ * - if we come here, then:
+ *   - the 'active count' _reached_ zero
+ *   - the 'waiting count' is non-zero
+ * - the spinlock must be held by the caller
+ * - woken process blocks are discarded from the list after having task zeroed
+ * - writers are only woken if wakewrite is non-zero
+ */
+static inline struct rw_semaphore *
+__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
+{
+	struct rwsem_waiter *waiter;
+	struct task_struct *tsk;
+	int woken;
+
+	rwsemtrace(sem, "Entering __rwsem_do_wake");
+
+	waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
+
+	if (!wakewrite) {
+		if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
+			goto out;
+		goto dont_wake_writers;
+	}
+
+	/* if we are allowed to wake writers try to grant a single write lock
+	 * if there's a writer at the front of the queue
+	 * - we leave the 'waiting count' incremented to signify potential
+	 *   contention
+	 */
+	if (waiter->flags & RWSEM_WAITING_FOR_WRITE) {
+		sem->activity = -1;
+		list_del(&waiter->list);
+		tsk = waiter->task;
+		/* Don't touch waiter after ->task has been NULLed */
+		mb();
+		waiter->task = NULL;
+		wake_up_process(tsk);
+		put_task_struct(tsk);
+		goto out;
+	}
+
+	/* grant an infinite number of read locks to the front of the queue */
+ dont_wake_writers:
+	woken = 0;
+	while (waiter->flags & RWSEM_WAITING_FOR_READ) {
+		struct list_head *next = waiter->list.next;
+
+		list_del(&waiter->list);
+		tsk = waiter->task;
+		mb();
+		waiter->task = NULL;
+		wake_up_process(tsk);
+		put_task_struct(tsk);
+		woken++;
+		if (list_empty(&sem->wait_list))
+			break;
+		waiter = list_entry(next, struct rwsem_waiter, list);
+	}
+
+	sem->activity += woken;
+
+ out:
+	rwsemtrace(sem, "Leaving __rwsem_do_wake");
+	return sem;
+}
+
+/*
+ * wake a single writer
+ */
+static inline struct rw_semaphore *
+__rwsem_wake_one_writer(struct rw_semaphore *sem)
+{
+	struct rwsem_waiter *waiter;
+	struct task_struct *tsk;
+
+	sem->activity = -1;
+
+	waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
+	list_del(&waiter->list);
+
+	tsk = waiter->task;
+	mb();
+	waiter->task = NULL;
+	wake_up_process(tsk);
+	put_task_struct(tsk);
+	return sem;
+}
+
+/*
+ * get a read lock on the semaphore
+ */
+void fastcall __sched __down_read(struct rw_semaphore *sem)
+{
+	struct rwsem_waiter waiter;
+	struct task_struct *tsk;
+
+	rwsemtrace(sem, "Entering __down_read");
+
+	spin_lock_irq(&sem->wait_lock);
+
+	if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
+		/* granted */
+		sem->activity++;
+		spin_unlock_irq(&sem->wait_lock);
+		goto out;
+	}
+
+	tsk = current;
+	set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+
+	/* set up my own style of waitqueue */
+	waiter.task = tsk;
+	waiter.flags = RWSEM_WAITING_FOR_READ;
+	get_task_struct(tsk);
+
+	list_add_tail(&waiter.list, &sem->wait_list);
+
+	/* we don't need to touch the semaphore struct anymore */
+	spin_unlock_irq(&sem->wait_lock);
+
+	/* wait to be given the lock */
+	for (;;) {
+		if (!waiter.task)
+			break;
+		schedule();
+		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+	}
+
+	tsk->state = TASK_RUNNING;
+
+ out:
+	rwsemtrace(sem, "Leaving __down_read");
+}
+
+/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+int fastcall __down_read_trylock(struct rw_semaphore *sem)
+{
+	unsigned long flags;
+	int ret = 0;
+
+	rwsemtrace(sem, "Entering __down_read_trylock");
+
+	spin_lock_irqsave(&sem->wait_lock, flags);
+
+	if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
+		/* granted */
+		sem->activity++;
+		ret = 1;
+	}
+
+	spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+	rwsemtrace(sem, "Leaving __down_read_trylock");
+	return ret;
+}
+
+/*
+ * get a write lock on the semaphore
+ * - we increment the waiting count anyway to indicate an exclusive lock
+ */
+void fastcall __sched __down_write(struct rw_semaphore *sem)
+{
+	struct rwsem_waiter waiter;
+	struct task_struct *tsk;
+
+	rwsemtrace(sem, "Entering __down_write");
+
+	spin_lock_irq(&sem->wait_lock);
+
+	if (sem->activity == 0 && list_empty(&sem->wait_list)) {
+		/* granted */
+		sem->activity = -1;
+		spin_unlock_irq(&sem->wait_lock);
+		goto out;
+	}
+
+	tsk = current;
+	set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+
+	/* set up my own style of waitqueue */
+	waiter.task = tsk;
+	waiter.flags = RWSEM_WAITING_FOR_WRITE;
+	get_task_struct(tsk);
+
+	list_add_tail(&waiter.list, &sem->wait_list);
+
+	/* we don't need to touch the semaphore struct anymore */
+	spin_unlock_irq(&sem->wait_lock);
+
+	/* wait to be given the lock */
+	for (;;) {
+		if (!waiter.task)
+			break;
+		schedule();
+		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+	}
+
+	tsk->state = TASK_RUNNING;
+
+ out:
+	rwsemtrace(sem, "Leaving __down_write");
+}
+
+/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+int fastcall __down_write_trylock(struct rw_semaphore *sem)
+{
+	unsigned long flags;
+	int ret = 0;
+
+	rwsemtrace(sem, "Entering __down_write_trylock");
+
+	spin_lock_irqsave(&sem->wait_lock, flags);
+
+	if (sem->activity == 0 && list_empty(&sem->wait_list)) {
+		/* granted */
+		sem->activity = -1;
+		ret = 1;
+	}
+
+	spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+	rwsemtrace(sem, "Leaving __down_write_trylock");
+	return ret;
+}
+
+/*
+ * release a read lock on the semaphore
+ */
+void fastcall __up_read(struct rw_semaphore *sem)
+{
+	unsigned long flags;
+
+	rwsemtrace(sem, "Entering __up_read");
+
+	spin_lock_irqsave(&sem->wait_lock, flags);
+
+	if (--sem->activity == 0 && !list_empty(&sem->wait_list))
+		sem = __rwsem_wake_one_writer(sem);
+
+	spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+	rwsemtrace(sem, "Leaving __up_read");
+}
+
+/*
+ * release a write lock on the semaphore
+ */
+void fastcall __up_write(struct rw_semaphore *sem)
+{
+	unsigned long flags;
+
+	rwsemtrace(sem, "Entering __up_write");
+
+	spin_lock_irqsave(&sem->wait_lock, flags);
+
+	sem->activity = 0;
+	if (!list_empty(&sem->wait_list))
+		sem = __rwsem_do_wake(sem, 1);
+
+	spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+	rwsemtrace(sem, "Leaving __up_write");
+}
+
+/*
+ * downgrade a write lock into a read lock
+ * - just wake up any readers at the front of the queue
+ */
+void fastcall __downgrade_write(struct rw_semaphore *sem)
+{
+	unsigned long flags;
+
+	rwsemtrace(sem, "Entering __downgrade_write");
+
+	spin_lock_irqsave(&sem->wait_lock, flags);
+
+	sem->activity = 1;
+	if (!list_empty(&sem->wait_list))
+		sem = __rwsem_do_wake(sem, 0);
+
+	spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+	rwsemtrace(sem, "Leaving __downgrade_write");
+}
+
+EXPORT_SYMBOL(init_rwsem);
+EXPORT_SYMBOL(__down_read);
+EXPORT_SYMBOL(__down_read_trylock);
+EXPORT_SYMBOL(__down_write);
+EXPORT_SYMBOL(__down_write_trylock);
+EXPORT_SYMBOL(__up_read);
+EXPORT_SYMBOL(__up_write);
+EXPORT_SYMBOL(__downgrade_write);
+#if RWSEM_DEBUG
+EXPORT_SYMBOL(rwsemtrace);
+#endif