Re: [PATCH 00/11] nested sleeps, fixes and debug infrastructure

Peter Zijlstra
2014-10-29T09:35:17Z

On Wed, Oct 29, 2014 at 01:00:56AM +0100, Oleg Nesterov wrote:
> On 10/28, Peter Zijlstra wrote:
> >
> > On Tue, Oct 28, 2014 at 01:07:03AM +0100, Oleg Nesterov wrote:
> >
> > > I was going to say that wait_event_freezable() in kauditd_thread()
> > > is not friendly wrt kthread_should_stop() and thus we we need
> > > kthread_freezable_should_stop().
> >
> > I'm not sure those two would interact, yes, both would first set either
> > the freezable or stop bit and then wake. If both were to race, all we
> > need to ensure is to check both before calling schedule again.
> >
> > A loop like:
> >
> > while (!kthread_should_stop()) {
> > wait_event_freezable(wq, cond);
> > }
> >
> > Would satisfy that, because even if kthread_should_stop() gets set first
> > and then freezing happens and we get into try_to_freeze() first, we'd
> > still to the kthread_should_stop() check right after we thaw.
>
> Right after, yes.
>
> But what if it calls try_to_freeze() and another thread (which should
> be frozen too) sleeps in kthread_stop() ?

Fair point indeed. Now I had a look at __refrigerator() and is there any
reason we should not remove that .check_kthr_stop argument and replace
it with an unconditional (current->flags & PF_KTHREAD) ?