[RFC PATCH-tip v2 4/6] locking/rwsem: move down rwsem_down_read_failed function

Waiman Long
2016-06-14T22:48:07Z

Move the rwsem_down_read_failed() function down to below the optimistic
spinning section before enabling optimistic spinning for the readers.
There is no change in code.

Signed-off-by: Waiman Long <Waiman.Long@hpe.com>
---
kernel/locking/rwsem-xadd.c | 116 +++++++++++++++++++++---------------------
1 files changed, 58 insertions(+), 58 deletions(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index adc2f44..c08c778 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -226,64 +226,6 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
}

/*
- * Wait for the read lock to be granted
- */
-__visible
-struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
-{
- long count, adjustment = 0;
- struct rwsem_waiter waiter;
- struct task_struct *tsk = current;
- WAKE_Q(wake_q);
-
- /*
- * Undo read bias from down_read operation, stop active locking.
- * Doing that after taking the wait_lock may block writer lock
- * stealing for too long.
- */
- atomic_long_add(-RWSEM_ACTIVE_READ_BIAS, &sem->count);
-
- /* set up my own style of waitqueue */
- waiter.task = tsk;
- waiter.type = RWSEM_WAITING_FOR_READ;
-
- 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 */
- if (adjustment)
- count = atomic_long_add_return(adjustment, &sem->count);
- else
- count = atomic_long_read(&sem->count);
-
- /* If there are no active locks, wake the front queued process(es).
- *
- * If there are no writers and we are first in the queue,
- * wake our own waiter to join the existing active readers !
- */
- if (count = RWSEM_WAITING_BIAS ||
- (count > RWSEM_WAITING_BIAS && adjustment))
- sem = __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
-
- raw_spin_unlock_irq(&sem->wait_lock);
- wake_up_q(&wake_q);
-
- /* wait to be given the lock */
- while (true) {
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
- if (!waiter.task)
- break;
- schedule();
- }
-
- __set_task_state(tsk, TASK_RUNNING);
- return sem;
-}
-EXPORT_SYMBOL(rwsem_down_read_failed);
-
-/*
* This function must be called with the sem->wait_lock held to prevent
* race conditions between checking the rwsem wait list and setting the
* sem->count accordingly.
@@ -505,6 +447,64 @@ static inline bool reader_spinning_enabled(struct rw_semaphore *sem)
#endif

/*
+ * Wait for the read lock to be granted
+ */
+__visible
+struct rw_semaphore __sched * rwsem_down_read_failed(struct rw_semaphore *sem)
+{
+ long count, adjustment = 0;
+ struct rwsem_waiter waiter;
+ struct task_struct *tsk = current;
+ WAKE_Q(wake_q);
+
+ /*
+ * Undo read bias from down_read operation, stop active locking.
+ * Doing that after taking the wait_lock may block writer lock
+ * stealing for too long.
+ */
+ atomic_long_add(-RWSEM_ACTIVE_READ_BIAS, &sem->count);
+
+ /* set up my own style of waitqueue */
+ waiter.task = tsk;
+ waiter.type = RWSEM_WAITING_FOR_READ;
+
+ 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 */
+ if (adjustment)
+ count = atomic_long_add_return(adjustment, &sem->count);
+ else
+ count = atomic_long_read(&sem->count);
+
+ /* If there are no active locks, wake the front queued process(es).
+ *
+ * If there are no writers and we are first in the queue,
+ * wake our own waiter to join the existing active readers !
+ */
+ if (count = RWSEM_WAITING_BIAS ||
+ (count > RWSEM_WAITING_BIAS && adjustment))
+ sem = __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+
+ raw_spin_unlock_irq(&sem->wait_lock);
+ wake_up_q(&wake_q);
+
+ /* wait to be given the lock */
+ while (true) {
+ set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ if (!waiter.task)
+ break;
+ schedule();
+ }
+
+ __set_task_state(tsk, TASK_RUNNING);
+ return sem;
+}
+EXPORT_SYMBOL(rwsem_down_read_failed);
+
+/*
* Wait until we successfully acquire the write lock
*/
static inline struct rw_semaphore *
--
1.7.1