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>
diff --git a/lib/rwsem.c b/lib/rwsem.c
index 0d50e46..9a675fa 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -68,20 +68,17 @@
signed long woken, loop, adjustment;
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
- if (waiter->type != RWSEM_WAITING_FOR_WRITE)
- goto readers_only;
-
- if (wake_type == RWSEM_WAKE_READ_OWNED)
- /* Another active reader was observed, so wakeup is not
- * likely to succeed. Save the atomic op.
- */
+ if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
+ if (wake_type != RWSEM_WAKE_READ_OWNED)
+ /* Wake writer at the front of the queue, but do not
+ * grant it the lock yet as we want other writers
+ * to be able to steal it. Readers, on the other hand,
+ * will block as they will notice the queued writer.
+ */
+ wake_up_process(waiter->task);
goto out;
+ }
- /* Wake up the writing waiter and let the task grab the sem: */
- wake_up_process(waiter->task);
- goto out;
-
- readers_only:
/* If we come here from up_xxxx(), another thread might have reached
* rwsem_down_failed_common() before we acquired the spinlock and
* woken up a waiter, making it now active. We prefer to check for
@@ -125,7 +122,8 @@
rwsem_atomic_add(adjustment, sem);
next = sem->wait_list.next;
- for (loop = woken; loop > 0; loop--) {
+ loop = woken;
+ do {
waiter = list_entry(next, struct rwsem_waiter, list);
next = waiter->list.next;
tsk = waiter->task;
@@ -133,7 +131,7 @@
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
- }
+ } while (--loop);
sem->wait_list.next = next;
next->prev = &sem->wait_list;