On Sun, 2010-09-19 at 15:09 +0200, Avi Kivity wrote:
> Some time ago, the i8259 emulation code in kvm was changed to use
> raw_spinlock_t, as it was called in a preempt_disable() and
> local_irq_disable() context, which doesn't work with preemptible
> spinlocks used with CONFIG_PREEMPT_RT.
>
> In Linux 2.6.37, the spinlock will no longer be taken in these contexts,
> so I'd like to change it to a normal spinlock_t. However, it is still
> taken in a spin_lock_irq() context.
>
> Is it okay to do this change? I figured since spin_lock_irq() is part
> of the spinlock infrastructure it might to the right thing.
>
In PREEMPT_RT all interrupts (besides the timer) is converted to a
thread. The spin_lock_irq() will not disable interrupts in PREEMPT_RT,
because it is not needed (irqs are threaded and wont cause a deadlock if
they share the same spin_locks).
Note, spin_locks used by the timer will must be raw_spin_lock(), and
threaded context must disable interrupts for real before using it.