linux-kernel - Re: [PATCH v3 2/4] KVM: use simple waitqueue for vcpu->wq

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Message-ID: <20151021111305.GL17308@twins.programming.kicks-ass.net>
Date:	Wed, 21 Oct 2015 13:13:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paul Mackerras <paulus@...abs.org>
Cc:	Daniel Wagner <daniel.wagner@...-carit.de>,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 2/4] KVM: use simple waitqueue for vcpu->wq

On Wed, Oct 21, 2015 at 08:24:11PM +1100, Paul Mackerras wrote:
> On Tue, Oct 20, 2015 at 04:00:31PM +0200, Peter Zijlstra wrote:
> > 
> > Should we not take this opportunity to get rid of these open-coded wait
> > loops?
> > 
> > 
> > Does this work?
> 
> No, on Book3S HV (POWER8) the VM hangs immediately after the kernel
> brings up all the secondary vCPUs, and is then unkillable.  I'm not
> sure what's wrong, although I wonder why you have TASK_IDLE rather
> than TASK_INTERRUPTIBLE in the ___wait_event call.

This was under the assumption that INTERRUPTIBLE was because you wanted
to avoid increasing load. Which was based on the lack of
signal_pending() tests near there (although there might have been in the
outermost loop which I overlooked).

If it does rely on signals, then this was obviously false and TASK_IDLE
is indeed wrong.


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