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From: Jan Kiszka on 23 Feb 2010 14:20
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.

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.

Jan

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From: Thomas Gleixner on 23 Feb 2010 17:30
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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