[PATCH] cfag12864b: Remove deprecated create_singlethread_workqueue

[PATCH] cfag12864b: Remove deprecated create_singlethread_workqueue

[Bhaktipriya Shridhar]

The workqueue has a single workitem(&cfag12864b_work) and hence doesn't
require ordering. Also, it is not being used on a memory reclaim path.
Hence, the singlethreaded workqueue has been replaced with the use of
system_wq.

System workqueues have been able to handle high level of concurrency
for a long time now and hence it's not required to have a singlethreaded
workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
created with create_singlethread_workqueue(), system_wq allows multiple
work items to overlap executions even on the same CPU; however, a
per-cpu workqueue doesn't have any CPU locality or global ordering
guarantee unless the target CPU is explicitly specified and thus the
increase of local concurrency shouldn't make any difference.

Work item has been cancelled in cfag12864b_disable() to ensure that
there are no pending tasks while disconnecting the driver.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
---
 drivers/auxdisplay/cfag12864b.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/drivers/auxdisplay/cfag12864b.c b/drivers/auxdisplay/cfag12864b.c
index 41ce4bd..46f380e 100644
--- a/drivers/auxdisplay/cfag12864b.c
+++ b/drivers/auxdisplay/cfag12864b.c
@@ -223,12 +223,11 @@ static unsigned char *cfag12864b_cache;
 static DEFINE_MUTEX(cfag12864b_mutex);
 static unsigned char cfag12864b_updating;
 static void cfag12864b_update(struct work_struct *delayed_work);
-static struct workqueue_struct *cfag12864b_workqueue;
 static DECLARE_DELAYED_WORK(cfag12864b_work, cfag12864b_update);

 static void cfag12864b_queue(void)
 {
-	queue_delayed_work(cfag12864b_workqueue, &cfag12864b_work,
+	schedule_delayed_work(&cfag12864b_work,
 		HZ / cfag12864b_rate);
 }

@@ -257,7 +256,6 @@ void cfag12864b_disable(void)
 	if (cfag12864b_updating) {
 		cfag12864b_updating = 0;
 		cancel_delayed_work(&cfag12864b_work);
-		flush_workqueue(cfag12864b_workqueue);
 	}

 	mutex_unlock(&cfag12864b_mutex);
@@ -357,19 +355,12 @@ static int __init cfag12864b_init(void)
 		goto bufferalloced;
 	}

-	cfag12864b_workqueue = create_singlethread_workqueue(CFAG12864B_NAME);
-	if (cfag12864b_workqueue == NULL)
-		goto cachealloced;
-
 	cfag12864b_clear();
 	cfag12864b_on();

 	cfag12864b_inited = 1;
 	return 0;

-cachealloced:
-	kfree(cfag12864b_cache);
-
 bufferalloced:
 	free_page((unsigned long) cfag12864b_buffer);

@@ -381,7 +372,6 @@ static void __exit cfag12864b_exit(void)
 {
 	cfag12864b_disable();
 	cfag12864b_off();
-	destroy_workqueue(cfag12864b_workqueue);
 	kfree(cfag12864b_cache);
 	free_page((unsigned long) cfag12864b_buffer);
 }
--
2.1.4

Re: [PATCH] cfag12864b: Remove deprecated create_singlethread_workqueue

[Tejun Heo]

On Tue, Jul 26, 2016 at 10:23:00PM +0530, Bhaktipriya Shridhar wrote:
> @@ -257,7 +256,6 @@ void cfag12864b_disable(void)
>  	if (cfag12864b_updating) {
>  		cfag12864b_updating = 0;
>  		cancel_delayed_work(&cfag12864b_work);
> -		flush_workqueue(cfag12864b_workqueue);

It should be converted to cancel_delayed_work_sync(); otherwise,
nothing guarantees that the work item is finished.

Thanks.

-- 
tejun