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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 22:20:36 (GMT)
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 22:20:36 (GMT)
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /lib/rwsem-spinlock.c
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'lib/rwsem-spinlock.c')
-rw-r--r--lib/rwsem-spinlock.c344
1 files changed, 344 insertions, 0 deletions
diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
new file mode 100644
index 0000000..21f0db2
--- /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

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