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!

1 files changed, 268 insertions, 0 deletions

diff --git a/lib/rwsem.c b/lib/rwsem.c
new file mode 100644
index 000000000000..7644089ec8fa
--- /dev/null
+++ b/lib/rwsem.c
@@ -0,0 +1,268 @@
+/* rwsem.c: R/W semaphores: contention handling functions
+ *
+ * Written by David Howells (dhowells@redhat.com).
+ * Derived from arch/i386/kernel/semaphore.c
+ */
+#include <linux/rwsem.h>
+#include <linux/sched.h>
+#include <linux/init.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
+#undef rwsemtrace
+void rwsemtrace(struct rw_semaphore *sem, const char *str)
+{
+        printk("sem=%p\n", sem);
+        printk("(sem)=%08lx\n", sem->count);
+        if (sem->debug)
+                printk("[%d] %s({%08lx})\n", current->pid, str, sem->count);
+}
+#endif
+
+/*
+ * handle the lock release when processes blocked on it that can now run
+ * - if we come here from up_xxxx(), then:
+ *   - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
+ *   - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
+ *   - there must be someone on the queue
+ * - 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 downgrading is false
+ */
+static inline struct rw_semaphore *
+__rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
+{
+        struct rwsem_waiter *waiter;
+        struct task_struct *tsk;
+        struct list_head *next;
+        signed long oldcount, woken, loop;
+
+        rwsemtrace(sem, "Entering __rwsem_do_wake");
+
+        if (downgrading)
+                goto dont_wake_writers;
+
+        /* if we came through an up_xxxx() call, we only only wake someone up
+         * if we can transition the active part of the count from 0 -> 1
+         */
+ try_again:
+        oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS, sem)
+                                                - RWSEM_ACTIVE_BIAS;
+        if (oldcount & RWSEM_ACTIVE_MASK)
+                goto undo;
+
+        waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
+
+        /* try to grant a single write lock if there's a writer at the front
+         * of the queue - note we leave the 'active part' of the count
+         * incremented by 1 and the waiting part incremented by 0x00010000
+         */
+        if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
+                goto readers_only;
+
+        /* We must be careful not to touch 'waiter' after we set ->task = NULL.
+         * It is an allocated on the waiter's stack and may become invalid at
+         * any time after that point (due to a wakeup from another source).
+         */
+        list_del(&waiter->list);
+        tsk = waiter->task;
+        mb();
+        waiter->task = NULL;
+        wake_up_process(tsk);
+        put_task_struct(tsk);
+        goto out;
+
+        /* don't want to wake any writers */
+ dont_wake_writers:
+        waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
+        if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
+                goto out;
+
+        /* grant an infinite number of read locks to the readers at the front
+         * of the queue
+         * - note we increment the 'active part' of the count by the number of
+         *   readers before waking any processes up
+         */
+ readers_only:
+        woken = 0;
+        do {
+                woken++;
+
+                if (waiter->list.next == &sem->wait_list)
+                        break;
+
+                waiter = list_entry(waiter->list.next,
+                                        struct rwsem_waiter, list);
+
+        } while (waiter->flags & RWSEM_WAITING_FOR_READ);
+
+        loop = woken;
+        woken *= RWSEM_ACTIVE_BIAS - RWSEM_WAITING_BIAS;
+        if (!downgrading)
+                /* we'd already done one increment earlier */
+                woken -= RWSEM_ACTIVE_BIAS;
+
+        rwsem_atomic_add(woken, sem);
+
+        next = sem->wait_list.next;
+        for (; loop > 0; loop--) {
+                waiter = list_entry(next, struct rwsem_waiter, list);
+                next = waiter->list.next;
+                tsk = waiter->task;
+                mb();
+                waiter->task = NULL;
+                wake_up_process(tsk);
+                put_task_struct(tsk);
+        }
+
+        sem->wait_list.next = next;
+        next->prev = &sem->wait_list;
+
+ out:
+        rwsemtrace(sem, "Leaving __rwsem_do_wake");
+        return sem;
+
+        /* undo the change to count, but check for a transition 1->0 */
+ undo:
+        if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) != 0)
+                goto out;
+        goto try_again;
+}
+
+/*
+ * wait for a lock to be granted
+ */
+static inline struct rw_semaphore *
+rwsem_down_failed_common(struct rw_semaphore *sem,
+                        struct rwsem_waiter *waiter, signed long adjustment)
+{
+        struct task_struct *tsk = current;
+        signed long count;
+
+        set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+
+        /* set up my own style of waitqueue */
+        spin_lock_irq(&sem->wait_lock);
+        waiter->task = tsk;
+        get_task_struct(tsk);
+
+        list_add_tail(&waiter->list, &sem->wait_list);
+
+        /* we're now waiting on the lock, but no longer actively read-locking */
+        count = rwsem_atomic_update(adjustment, sem);
+
+        /* if there are no active locks, wake the front queued process(es) up */
+        if (!(count & RWSEM_ACTIVE_MASK))
+                sem = __rwsem_do_wake(sem, 0);
+
+        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;
+
+        return sem;
+}
+
+/*
+ * wait for the read lock to be granted
+ */
+struct rw_semaphore fastcall __sched *
+rwsem_down_read_failed(struct rw_semaphore *sem)
+{
+        struct rwsem_waiter waiter;
+
+        rwsemtrace(sem, "Entering rwsem_down_read_failed");
+
+        waiter.flags = RWSEM_WAITING_FOR_READ;
+        rwsem_down_failed_common(sem, &waiter,
+                                RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS);
+
+        rwsemtrace(sem, "Leaving rwsem_down_read_failed");
+        return sem;
+}
+
+/*
+ * wait for the write lock to be granted
+ */
+struct rw_semaphore fastcall __sched *
+rwsem_down_write_failed(struct rw_semaphore *sem)
+{
+        struct rwsem_waiter waiter;
+
+        rwsemtrace(sem, "Entering rwsem_down_write_failed");
+
+        waiter.flags = RWSEM_WAITING_FOR_WRITE;
+        rwsem_down_failed_common(sem, &waiter, -RWSEM_ACTIVE_BIAS);
+
+        rwsemtrace(sem, "Leaving rwsem_down_write_failed");
+        return sem;
+}
+
+/*
+ * handle waking up a waiter on the semaphore
+ * - up_read/up_write has decremented the active part of count if we come here
+ */
+struct rw_semaphore fastcall *rwsem_wake(struct rw_semaphore *sem)
+{
+        unsigned long flags;
+
+        rwsemtrace(sem, "Entering rwsem_wake");
+
+        spin_lock_irqsave(&sem->wait_lock, flags);
+
+        /* do nothing if list empty */
+        if (!list_empty(&sem->wait_list))
+                sem = __rwsem_do_wake(sem, 0);
+
+        spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+        rwsemtrace(sem, "Leaving rwsem_wake");
+
+        return sem;
+}
+
+/*
+ * downgrade a write lock into a read lock
+ * - caller incremented waiting part of count and discovered it still negative
+ * - just wake up any readers at the front of the queue
+ */
+struct rw_semaphore fastcall *rwsem_downgrade_wake(struct rw_semaphore *sem)
+{
+        unsigned long flags;
+
+        rwsemtrace(sem, "Entering rwsem_downgrade_wake");
+
+        spin_lock_irqsave(&sem->wait_lock, flags);
+
+        /* do nothing if list empty */
+        if (!list_empty(&sem->wait_list))
+                sem = __rwsem_do_wake(sem, 1);
+
+        spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+        rwsemtrace(sem, "Leaving rwsem_downgrade_wake");
+        return sem;
+}
+
+EXPORT_SYMBOL(rwsem_down_read_failed);
+EXPORT_SYMBOL(rwsem_down_write_failed);
+EXPORT_SYMBOL(rwsem_wake);
+EXPORT_SYMBOL(rwsem_downgrade_wake);
+#if RWSEM_DEBUG
+EXPORT_SYMBOL(rwsemtrace);
+#endif