locking: Move the rwsem code to kernel/locking/

Notably: changed lib/rwsem* targets from lib- to obj-, no idea about
the ramifications of that.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-g0kynfh5feriwc6p3h6kpbw6@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 296 insertions, 0 deletions

diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
new file mode 100644
index 000000000000..9be8a9144978
--- /dev/null
+++ b/kernel/locking/rwsem-spinlock.c
@@ -0,0 +1,296 @@
+/* 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/export.h>
+
+enum rwsem_waiter_type {
+        RWSEM_WAITING_FOR_WRITE,
+        RWSEM_WAITING_FOR_READ
+};
+
+struct rwsem_waiter {
+        struct list_head list;
+        struct task_struct *task;
+        enum rwsem_waiter_type type;
+};
+
+int rwsem_is_locked(struct rw_semaphore *sem)
+{
+        int ret = 1;
+        unsigned long flags;
+
+        if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) {
+                ret = (sem->activity != 0);
+                raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+        }
+        return ret;
+}
+EXPORT_SYMBOL(rwsem_is_locked);
+
+/*
+ * initialise the semaphore
+ */
+void __init_rwsem(struct rw_semaphore *sem, const char *name,
+                  struct lock_class_key *key)
+{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+        /*
+         * Make sure we are not reinitializing a held semaphore:
+         */
+        debug_check_no_locks_freed((void *)sem, sizeof(*sem));
+        lockdep_init_map(&sem->dep_map, name, key, 0);
+#endif
+        sem->activity = 0;
+        raw_spin_lock_init(&sem->wait_lock);
+        INIT_LIST_HEAD(&sem->wait_list);
+}
+EXPORT_SYMBOL(__init_rwsem);
+
+/*
+ * 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;
+
+        waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
+
+        if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
+                if (wakewrite)
+                        /* Wake up a writer. Note that we do not grant it the
+                         * lock - it will have to acquire it when it runs. */
+                        wake_up_process(waiter->task);
+                goto out;
+        }
+
+        /* grant an infinite number of read locks to the front of the queue */
+        woken = 0;
+        do {
+                struct list_head *next = waiter->list.next;
+
+                list_del(&waiter->list);
+                tsk = waiter->task;
+                smp_mb();
+                waiter->task = NULL;
+                wake_up_process(tsk);
+                put_task_struct(tsk);
+                woken++;
+                if (next == &sem->wait_list)
+                        break;
+                waiter = list_entry(next, struct rwsem_waiter, list);
+        } while (waiter->type != RWSEM_WAITING_FOR_WRITE);
+
+        sem->activity += woken;
+
+ out:
+        return sem;
+}
+
+/*
+ * wake a single writer
+ */
+static inline struct rw_semaphore *
+__rwsem_wake_one_writer(struct rw_semaphore *sem)
+{
+        struct rwsem_waiter *waiter;
+
+        waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
+        wake_up_process(waiter->task);
+
+        return sem;
+}
+
+/*
+ * get a read lock on the semaphore
+ */
+void __sched __down_read(struct rw_semaphore *sem)
+{
+        struct rwsem_waiter waiter;
+        struct task_struct *tsk;
+        unsigned long flags;
+
+        raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+        if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
+                /* granted */
+                sem->activity++;
+                raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+                goto out;
+        }
+
+        tsk = current;
+        set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+
+        /* set up my own style of waitqueue */
+        waiter.task = tsk;
+        waiter.type = 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 */
+        raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+        /* wait to be given the lock */
+        for (;;) {
+                if (!waiter.task)
+                        break;
+                schedule();
+                set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+        }
+
+        tsk->state = TASK_RUNNING;
+ out:
+        ;
+}
+
+/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+int __down_read_trylock(struct rw_semaphore *sem)
+{
+        unsigned long flags;
+        int ret = 0;
+
+
+        raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+        if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
+                /* granted */
+                sem->activity++;
+                ret = 1;
+        }
+
+        raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+        return ret;
+}
+
+/*
+ * get a write lock on the semaphore
+ */
+void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
+{
+        struct rwsem_waiter waiter;
+        struct task_struct *tsk;
+        unsigned long flags;
+
+        raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+        /* set up my own style of waitqueue */
+        tsk = current;
+        waiter.task = tsk;
+        waiter.type = RWSEM_WAITING_FOR_WRITE;
+        list_add_tail(&waiter.list, &sem->wait_list);
+
+        /* wait for someone to release the lock */
+        for (;;) {
+                /*
+                 * That is the key to support write lock stealing: allows the
+                 * task already on CPU to get the lock soon rather than put
+                 * itself into sleep and waiting for system woke it or someone
+                 * else in the head of the wait list up.
+                 */
+                if (sem->activity == 0)
+                        break;
+                set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+                raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+                schedule();
+                raw_spin_lock_irqsave(&sem->wait_lock, flags);
+        }
+        /* got the lock */
+        sem->activity = -1;
+        list_del(&waiter.list);
+
+        raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+}
+
+void __sched __down_write(struct rw_semaphore *sem)
+{
+        __down_write_nested(sem, 0);
+}
+
+/*
+ * trylock for writing -- returns 1 if successful, 0 if contention
+ */
+int __down_write_trylock(struct rw_semaphore *sem)
+{
+        unsigned long flags;
+        int ret = 0;
+
+        raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+        if (sem->activity == 0) {
+                /* got the lock */
+                sem->activity = -1;
+                ret = 1;
+        }
+
+        raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+        return ret;
+}
+
+/*
+ * release a read lock on the semaphore
+ */
+void __up_read(struct rw_semaphore *sem)
+{
+        unsigned long flags;
+
+        raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+        if (--sem->activity == 0 && !list_empty(&sem->wait_list))
+                sem = __rwsem_wake_one_writer(sem);
+
+        raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+}
+
+/*
+ * release a write lock on the semaphore
+ */
+void __up_write(struct rw_semaphore *sem)
+{
+        unsigned long flags;
+
+        raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+        sem->activity = 0;
+        if (!list_empty(&sem->wait_list))
+                sem = __rwsem_do_wake(sem, 1);
+
+        raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+}
+
+/*
+ * downgrade a write lock into a read lock
+ * - just wake up any readers at the front of the queue
+ */
+void __downgrade_write(struct rw_semaphore *sem)
+{
+        unsigned long flags;
+
+        raw_spin_lock_irqsave(&sem->wait_lock, flags);
+
+        sem->activity = 1;
+        if (!list_empty(&sem->wait_list))
+                sem = __rwsem_do_wake(sem, 0);
+
+        raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+}
+