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

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Message-ID: <20141029093503.GX3337@twins.programming.kicks-ass.net>
Date:	Wed, 29 Oct 2014 10:35:03 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>, mingo@...nel.org,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	ilya.dryomov@...tank.com, linux-kernel@...r.kernel.org,
	Eric Paris <eparis@...hat.com>, rafael.j.wysocki@...el.com
Subject: Re: [PATCH 00/11] nested sleeps, fixes and debug infrastructure

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) ?
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