rwsem: simplify rwsem_down_read_failed
When trying to acquire a read lock, the RWSEM_ACTIVE_READ_BIAS
adjustment doesn't cause other readers to block, so we never have to
worry about waking them back after canceling this adjustment in
rwsem_down_read_failed().
We also never want to steal the lock in rwsem_down_read_failed(), so we
don't have to grab the wait_lock either.
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>
diff --git a/lib/rwsem.c b/lib/rwsem.c
index fb658af..66f307e 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -182,7 +182,6 @@
*/
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;
@@ -190,7 +189,7 @@
/* set up my own style of waitqueue */
waiter.task = tsk;
- waiter.type = type;
+ waiter.type = RWSEM_WAITING_FOR_READ;
get_task_struct(tsk);
raw_spin_lock_irq(&sem->wait_lock);
@@ -201,17 +200,9 @@
/* 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 there are no active locks, wake the front queued process(es). */
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);
@@ -220,15 +211,6 @@
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();
}
