[PATCH v2 0/2] Remove improper workqueue usage

[PATCH v2 0/2] Remove improper workqueue usage

[Bhaktipriya Shridhar]

This patch set fixes the improper usage of the workqueue API.
This includes dropping the freeing of workqueue and removing the
deprecated create_singlethread_workqueue instance.

Bhaktipriya Shridhar (2):
  [media] cx25821: Drop Freeing of Workqueue
  [media] cx25821: Remove deprecated create_singlethread_workqueue

 drivers/media/pci/cx25821/cx25821-audio-upstream.c | 14 ++------------
 drivers/media/pci/cx25821/cx25821.h                |  1 -
 2 files changed, 2 insertions(+), 13 deletions(-)

--
2.1.4

[PATCH v2 1/2] [media] cx25821: Drop Freeing of Workqueue

[Bhaktipriya Shridhar]

Workqueues shouldn't be freed. destroy_workqueue should be used instead.
destroy_workqueue safely destroys a workqueue and ensures that all pending
work items are done before destroying the workqueue.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
---
 Changes in v2: None

 drivers/media/pci/cx25821/cx25821-audio-upstream.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/pci/cx25821/cx25821-audio-upstream.c b/drivers/media/pci/cx25821/cx25821-audio-upstream.c
index 68dbc2d..05bd957 100644
--- a/drivers/media/pci/cx25821/cx25821-audio-upstream.c
+++ b/drivers/media/pci/cx25821/cx25821-audio-upstream.c
@@ -242,7 +242,7 @@ void cx25821_stop_upstream_audio(struct cx25821_dev *dev)
 	dev->_audioframe_count = 0;
 	dev->_audiofile_status = END_OF_FILE;

-	kfree(dev->_irq_audio_queues);
+	destroy_workqueue(dev->_irq_audio_queues);
 	dev->_irq_audio_queues = NULL;

 	kfree(dev->_audiofilename);
--
2.1.4

[PATCH v2 2/2] [media] cx25821: Remove deprecated create_singlethread_workqueue

[Bhaktipriya Shridhar]

The workqueue "_irq_audio_queues" runs the audio upstream handler.
It has a single work item(&dev->_audio_work_entry) 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.

The work item has been flushed in cx25821_stop_upstream_audio() to ensure
that nothing is pending when the driver is disconnected.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
---
 Changes in v2:
	-Flushed work item and updated the commit description to reflect
	 the same.

 drivers/media/pci/cx25821/cx25821-audio-upstream.c | 14 ++------------
 drivers/media/pci/cx25821/cx25821.h                |  1 -
 2 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/drivers/media/pci/cx25821/cx25821-audio-upstream.c b/drivers/media/pci/cx25821/cx25821-audio-upstream.c
index 05bd957..7c8edb6 100644
--- a/drivers/media/pci/cx25821/cx25821-audio-upstream.c
+++ b/drivers/media/pci/cx25821/cx25821-audio-upstream.c
@@ -242,8 +242,7 @@ void cx25821_stop_upstream_audio(struct cx25821_dev *dev)
 	dev->_audioframe_count = 0;
 	dev->_audiofile_status = END_OF_FILE;

-	destroy_workqueue(dev->_irq_audio_queues);
-	dev->_irq_audio_queues = NULL;
+	flush_work(&dev->_audio_work_entry);

 	kfree(dev->_audiofilename);
 }
@@ -446,8 +445,7 @@ static int cx25821_audio_upstream_irq(struct cx25821_dev *dev, int chan_num,

 			dev->_audioframe_index = dev->_last_index_irq;

-			queue_work(dev->_irq_audio_queues,
-				   &dev->_audio_work_entry);
+			schedule_work(&dev->_audio_work_entry);
 		}

 		if (dev->_is_first_audio_frame) {
@@ -639,14 +637,6 @@ int cx25821_audio_upstream_init(struct cx25821_dev *dev, int channel_select)

 	/* Work queue */
 	INIT_WORK(&dev->_audio_work_entry, cx25821_audioups_handler);
-	dev->_irq_audio_queues =
-	    create_singlethread_workqueue("cx25821_audioworkqueue");
-
-	if (!dev->_irq_audio_queues) {
-		printk(KERN_DEBUG
-			pr_fmt("ERROR: create_singlethread_workqueue() for Audio FAILED!\n"));
-		return -ENOMEM;
-	}

 	dev->_last_index_irq = 0;
 	dev->_audio_is_running = 0;
diff --git a/drivers/media/pci/cx25821/cx25821.h b/drivers/media/pci/cx25821/cx25821.h
index a513b68..c813d88 100644
--- a/drivers/media/pci/cx25821/cx25821.h
+++ b/drivers/media/pci/cx25821/cx25821.h
@@ -294,7 +294,6 @@ struct cx25821_dev {
 	u32 audio_upstream_riscbuf_size;
 	u32 audio_upstream_databuf_size;
 	int _audioframe_index;
-	struct workqueue_struct *_irq_audio_queues;
 	struct work_struct _audio_work_entry;
 	char *input_audiofilename;

--
2.1.4

Re: [PATCH v2 1/2] [media] cx25821: Drop Freeing of Workqueue

[Tejun Heo]

On Mon, Jul 25, 2016 at 08:25:22PM +0530, Bhaktipriya Shridhar wrote:
> Workqueues shouldn't be freed. destroy_workqueue should be used instead.
> destroy_workqueue safely destroys a workqueue and ensures that all pending
> work items are done before destroying the workqueue.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>

Acked-by: Tejun Heo <tj@kernel.org>

Mauro, can you please pick this one up?  It prolly should be tagged
for -stable too.

Thanks.

-- 
tejun