Linux Virtualization - Nov 2014 - [PATCH v3] virtio_balloon: Convert "vballoon" kthread into a workqueue

On Thu, Nov 20, 2014 at 11:07:46AM -0500, Tejun Heo
wrote:
> On Thu, Nov 20, 2014 at 05:03:17PM +0100, Petr Mladek wrote:
> ...
> > @@ -476,7 +460,6 @@ static void virtballoon_remove(struct
virtio_device *vdev)
> >  {
> >  	struct virtio_balloon *vb = vdev->priv;
> >  
> > -	kthread_stop(vb->thread);
> >  	remove_common(vb);
> >  	kfree(vb);
> >  }
> 
> Shouldn't the work item be flushed before removal is complete?
In fact, flushing it won't help because it can requeue itself, right?

> Thanks.
> 
> -- 
> tejun

On Thu, Nov 20, 2014 at 06:25:43PM +0200, Michael S. Tsirkin
wrote:
> On Thu, Nov 20, 2014 at 11:07:46AM -0500, Tejun Heo wrote:
> > On Thu, Nov 20, 2014 at 05:03:17PM +0100, Petr Mladek wrote:
> > ...
> > > @@ -476,7 +460,6 @@ static void virtballoon_remove(struct
virtio_device *vdev)
> > >  {
> > >  	struct virtio_balloon *vb = vdev->priv;
> > >  
> > > -	kthread_stop(vb->thread);
> > >  	remove_common(vb);
> > >  	kfree(vb);
> > >  }
> > 
> > Shouldn't the work item be flushed before removal is complete?
> 
> In fact, flushing it won't help because it can requeue itself, right?
>From that POV a dedicated WQ kept it simple.
> 
> > Thanks.
> > 
> > -- 
> > tejun

On Thu, Nov 20, 2014 at 06:26:24PM +0200, Michael S. Tsirkin
wrote:
> On Thu, Nov 20, 2014 at 06:25:43PM +0200, Michael S. Tsirkin wrote:
> > On Thu, Nov 20, 2014 at 11:07:46AM -0500, Tejun Heo wrote:
> > > On Thu, Nov 20, 2014 at 05:03:17PM +0100, Petr Mladek wrote:
> > > ...
> > > > @@ -476,7 +460,6 @@ static void virtballoon_remove(struct
virtio_device *vdev)
> > > >  {
> > > >  	struct virtio_balloon *vb = vdev->priv;
> > > >  
> > > > -	kthread_stop(vb->thread);
> > > >  	remove_common(vb);
> > > >  	kfree(vb);
> > > >  }
> > > 
> > > Shouldn't the work item be flushed before removal is
complete?
> > 
> > In fact, flushing it won't help because it can requeue itself,
right?
There's cancel_work_sync() to stop the self-requeueing ones.
> From that POV a dedicated WQ kept it simple.
A dedicated wq doesn't do anything for that.  You can't shut down a
workqueue with a pending work item on it.  destroy_workqueue() will
try to drain the target wq, warn if it doesn't finish in certain
number of iterations and just keep trying indefinitely.

Thanks.

-- 
tejun