rwsem: move rwsem_down_failed_common code into rwsem_down_{read,write}_failed

Remove the rwsem_down_failed_common function and replace it with two
identical copies of its code in rwsem_down_{read,write}_failed.

This is because we want to make different optimizations in
rwsem_down_{read,write}_failed; we are adding this pure-duplication
step as a separate commit in order to make it easier to check the
following steps.

Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 57 insertions, 15 deletions

diff --git a/lib/rwsem.c b/lib/rwsem.c
index 40636454cf3c..fb658af1c12c 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -178,12 +178,12 @@ try_again_write:
 }
 
 /*
- * wait for a lock to be granted
+ * wait for the read lock to be granted
  */
-static struct rw_semaphore __sched *
-rwsem_down_failed_common(struct rw_semaphore *sem,
-                         enum rwsem_waiter_type type, signed long adjustment)
+struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
 {
+        enum rwsem_waiter_type type = RWSEM_WAITING_FOR_READ;
+        signed long adjustment = -RWSEM_ACTIVE_READ_BIAS;
         struct rwsem_waiter waiter;
         struct task_struct *tsk = current;
         signed long count;
@@ -238,21 +238,63 @@ rwsem_down_failed_common(struct rw_semaphore *sem,
 }
 
 /*
- * wait for the read lock to be granted
- */
-struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
-{
-        return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_READ,
-                                        -RWSEM_ACTIVE_READ_BIAS);
-}
-
-/*
  * wait for the write lock to be granted
  */
 struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
 {
-        return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_WRITE,
-                                        -RWSEM_ACTIVE_WRITE_BIAS);
+        enum rwsem_waiter_type type = RWSEM_WAITING_FOR_WRITE;
+        signed long adjustment = -RWSEM_ACTIVE_WRITE_BIAS;
+        struct rwsem_waiter waiter;
+        struct task_struct *tsk = current;
+        signed long count;
+
+        /* set up my own style of waitqueue */
+        waiter.task = tsk;
+        waiter.type = type;
+        get_task_struct(tsk);
+
+        raw_spin_lock_irq(&sem->wait_lock);
+        if (list_empty(&sem->wait_list))
+                adjustment += RWSEM_WAITING_BIAS;
+        list_add_tail(&waiter.list, &sem->wait_list);
+
+        /* we're now waiting on the lock, but no longer actively locking */
+        count = rwsem_atomic_update(adjustment, sem);
+
+        /* If there are no active locks, wake the front queued process(es) up.
+         *
+         * Alternatively, if we're called from a failed down_write(), there
+         * were already threads queued before us and there are no active
+         * writers, the lock must be read owned; so we try to wake any read
+         * locks that were queued ahead of us. */
+        if (count == RWSEM_WAITING_BIAS)
+                sem = __rwsem_do_wake(sem, RWSEM_WAKE_NO_ACTIVE);
+        else if (count > RWSEM_WAITING_BIAS &&
+                 adjustment == -RWSEM_ACTIVE_WRITE_BIAS)
+                sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED);
+
+        raw_spin_unlock_irq(&sem->wait_lock);
+
+        /* wait to be given the lock */
+        while (true) {
+                set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+                if (!waiter.task)
+                        break;
+
+                raw_spin_lock_irq(&sem->wait_lock);
+                /* Try to get the writer sem, may steal from the head writer: */
+                if (type == RWSEM_WAITING_FOR_WRITE)
+                        if (try_get_writer_sem(sem, &waiter)) {
+                                raw_spin_unlock_irq(&sem->wait_lock);
+                                return sem;
+                        }
+                raw_spin_unlock_irq(&sem->wait_lock);
+                schedule();
+        }
+
+        tsk->state = TASK_RUNNING;
+
+        return sem;
 }
 
 /*