1 files changed, 344 insertions, 0 deletions

diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
new file mode 100644
index 000000000000..21f0db2c9711
--- /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