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[PATCH-tip 2/3] locking/rwsem: move down rwsem_down_read_failed()

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  [PATCH-tip 2/3] locking/rwsem: move down rwsem_down_read_failed() Waiman Long <longman@redhat.com> - 2017-02-22 19:10 +0100
    Re: [PATCH-tip 2/3] locking/rwsem: move down rwsem_down_read_failed() Davidlohr Bueso <dave@stgolabs.net> - 2017-02-26 21:30 +0100
      Re: [PATCH-tip 2/3] locking/rwsem: move down rwsem_down_read_failed() Waiman Long <longman@redhat.com> - 2017-02-27 15:50 +0100

#1586359 — [PATCH-tip 2/3] locking/rwsem: move down rwsem_down_read_failed()

Move the rwsem_down_read_failed() function down to below the
optimistic spinning section as it is going to use function in that
section in a later patch.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/locking/rwsem-xadd.c | 96 ++++++++++++++++++++++-----------------------
 1 file changed, 48 insertions(+), 48 deletions(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index b5d7055..fb6d6f3 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -219,54 +219,6 @@ static void __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 = -RWSEM_ACTIVE_READ_BIAS;
-	struct rwsem_waiter waiter;
-	DEFINE_WAKE_Q(wake_q);
-
-	waiter.task = current;
-	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, but no longer actively locking */
-	count = atomic_long_add_return(adjustment, &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 != -RWSEM_ACTIVE_READ_BIAS))
-		__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_current_state(TASK_UNINTERRUPTIBLE);
-		if (!waiter.task)
-			break;
-		schedule();
-	}
-
-	__set_current_state(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.
@@ -461,6 +413,54 @@ static inline bool rwsem_has_spinner(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 = -RWSEM_ACTIVE_READ_BIAS;
+	struct rwsem_waiter waiter;
+	DEFINE_WAKE_Q(wake_q);
+
+	waiter.task = current;
+	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, but no longer actively locking */
+	count = atomic_long_add_return(adjustment, &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 != -RWSEM_ACTIVE_READ_BIAS))
+		__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_current_state(TASK_UNINTERRUPTIBLE);
+		if (!waiter.task)
+			break;
+		schedule();
+	}
+
+	__set_current_state(TASK_RUNNING);
+	return sem;
+}
+EXPORT_SYMBOL(rwsem_down_read_failed);
+
+/*
  * Wait until we successfully acquire the write lock
  */
 static inline struct rw_semaphore *
-- 
1.8.3.1

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#1588391

On Wed, 22 Feb 2017, Waiman Long wrote:

>Move the rwsem_down_read_failed() function down to below the
>optimistic spinning section as it is going to use function in that
>section in a later patch.

So the title is a bit ambiguous, and I would argue that this
should be folded into patch 3, and just mention it in the
changelog.

Thanks,
Davidlohr

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#1588699

On 02/26/2017 01:33 PM, Davidlohr Bueso wrote:
> On Wed, 22 Feb 2017, Waiman Long wrote:
>
>> Move the rwsem_down_read_failed() function down to below the
>> optimistic spinning section as it is going to use function in that
>> section in a later patch.
>
> So the title is a bit ambiguous, and I would argue that this
> should be folded into patch 3, and just mention it in the
> changelog.
>
> Thanks,
> Davidlohr

I can reword the title to clarify it a bit more.

The reason why it is a separate patch is because it will make it much
harder to review the third patch otherwise. What you get from the diff
will be a total replacement of one function block by another function
block. I would like to make the review focus on what is actually being
changed.

Cheers,
Longman

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