Re: [PATCH UPDATED 1/3] vhost: replace vhost_workqueue with per-vhost kthread

Michael S. Tsirkin
2010-07-26T16:37:16Z

On Mon, Jul 26, 2010 at 06:14:30PM +0200, Tejun Heo wrote:
> Just one more thing.
>
> On 07/26/2010 06:05 PM, Tejun Heo wrote:
> > * Placing try_to_freeze() could be a bit annoying. It shouldn't be
> > executed when there's a work to flush.

BTW why is this important?
We could always get another work and flush right after
try_to_freeze, and then flush would block for a long time.

BTW the vhost patch you sent does not do this at all.
I am guessing it is because our thread is not freezable?

> * Similar issue exists for kthread_stop(). The kthread shouldn't exit
> while there's a work to flush (please note that kthread_worker
> interface allows detaching / attaching worker kthread during
> operation, so it should remain in consistent state with regard to
> flushing).
>
> Thanks.

Not sure I agree here. Users must synchronise flush and stop calls.
Otherwise a work might get queued after stop is called, and
you won't be able to flush it.

> --
> tejun