rwsem: simplify __rwsem_do_wake

This is mostly for cleanup value:

- We don't need several gotos to handle the case where the first
  waiter is a writer. Two simple tests will do (and generate very
  similar code).

- In the remainder of the function, we know the first waiter is a reader,
  so we don't have to double check that. We can use do..while loops
  to iterate over the readers to wake (generates slightly better code).

Signed-off-by: Michel Lespinasse <walken@google.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, 7 insertions, 16 deletions

diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
index 5f117f37ac0a..9be8a9144978 100644
--- a/lib/rwsem-spinlock.c
+++ b/lib/rwsem-spinlock.c
@@ -70,26 +70,17 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
 
         waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
 
-        if (!wakewrite) {
-                if (waiter->type == RWSEM_WAITING_FOR_WRITE)
-                        goto out;
-                goto dont_wake_writers;
-        }
-
-        /*
-         * as we support write lock stealing, we can't set sem->activity
-         * to -1 here to indicate we get the lock. Instead, we wake it up
-         * to let it go get it again.
-         */
         if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
-                wake_up_process(waiter->task);
+                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 */
- dont_wake_writers:
         woken = 0;
-        while (waiter->type == RWSEM_WAITING_FOR_READ) {
+        do {
                 struct list_head *next = waiter->list.next;
 
                 list_del(&waiter->list);
@@ -99,10 +90,10 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
                 wake_up_process(tsk);
                 put_task_struct(tsk);
                 woken++;
-                if (list_empty(&sem->wait_list))
+                if (next == &sem->wait_list)
                         break;
                 waiter = list_entry(next, struct rwsem_waiter, list);
-        }
+        } while (waiter->type != RWSEM_WAITING_FOR_WRITE);
 
         sem->activity += woken;