Messages in this thread | | | Date | Thu, 20 Nov 2014 17:55:58 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH v3] virtio_balloon: Convert "vballoon" kthread into a workqueue |
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On Thu 2014-11-20 11:29:35, Tejun Heo wrote: > 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?
Great catch!
> > > In fact, flushing it won't help because it can requeue itself, right? > > There's cancel_work_sync() to stop the self-requeueing ones.
Ah, one more problem is that remove_common(vb) calls leak_balloon() that queues the work if not finished. We would need to add some flag or variant that would disable the queuing when called here.
> > 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.
I wonder if it is guaranteed that none would trigger stats_request() or virtballoon_changed() when virtballoon_remove() is being called. I guess so because the original code would fail otherwise. The two functions access "vb->config_change" and the structure is freed in virtballoon_remove() without any protection.
I am trying to confirm this by reading the code but it is not that easy.
Best Regards, Petr
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