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 5f117f37ac0..9be8a914497 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;