Re: [PATCH 2/3] workqueue: not allow recursion run_workqueue

[Oleg Nesterov <oleg@redhat.com>]

On 01/22, Frederic Weisbecker wrote:
>
> On Thu, Jan 22, 2009 at 05:14:24PM +0800, Lai Jiangshan wrote:
> >  static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
> >  {
> > -	int active;
> > +	int active = 0;
> > +	struct wq_barrier barr;
> >
> > -	if (cwq->thread == current) {
> > -		/*
> > -		 * Probably keventd trying to flush its own queue. So simply run
> > -		 * it by hand rather than deadlocking.
> > -		 */
> > -		run_workqueue(cwq);
> > -		active = 1;
> > -	} else {
> > -		struct wq_barrier barr;
> > +	BUG_ON(cwq->thread == current);
>
> Hi Lai,
>
> BUG_ON seems perhaps a bit too much for such case. The system
> will run in an endless loop because of a mistake that will not have
> necessarily a fatal end.

Confused. Why do you think the system will run in an endless loop?
cwq-thread will exit.

> WARN_ON should be enough (plus the warn that lockdep will raise
> too in this case).

and if cwq-thread proceeds after WARN_ON() it will be "lost" anyway
because it will sleep forever.

Not that I think BUG_ON() is much better, except it is more "loud".


As for the patch itself, I completely agree with Peter.

Oleg.