linux-kernel - Re: [patch] x86: kvm: Convert i8254/i8259 locks to raw

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Date:	Tue, 23 Feb 2010 23:23:37 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jan Kiszka <jan.kiszka@...mens.com>
cc:	Avi Kivity <avi@...hat.com>, KVM <kvm@...r.kernel.org>,
	Gleb Natapov <gleb@...hat.com>,
	RT <linux-rt-users@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch] x86: kvm: Convert i8254/i8259 locks to raw_spinlocks

On Tue, 23 Feb 2010, Jan Kiszka wrote:

> Thomas Gleixner wrote:
> > The i8254/i8259 locks need to be real spinlocks on preempt-rt. Convert
> > them to raw_spinlock. No change for !RT kernels.
> 
> Doesn't fly for -rt anymore: pic_irq_update runs under this raw lock and
> calls kvm_vcpu_kick which tries to wake_up some thread -> scheduling
> while atomic.

Hmm, a wakeup itself is fine. Is that code waking a wake queue ?
 
> This used to work up to 956f97cf. -rt for 2.6.31 is not yet affected,
> but 2.6.33 should be broken (haven't checked, using kvm-kmod over 2.6.31
> ATM). I can provide a patch that restores the deferred kicking if it's
> acceptable for upstream.

Well, at least is would be nice to have one for -rt.

Thanks,

	tglx
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