linux-kernel - Re: [PATCH] mips/rt: convert cascade interrupt non threaded

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Date:	Thu, 1 Sep 2011 21:20:01 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Liming Wang <liming.wang@...driver.com>
cc:	rt-users <linux-rt-users@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mips/rt: convert cascade interrupt non threaded

On Fri, 26 Aug 2011, Liming Wang wrote:

> The preempt_rt kernel forces all irq interrupts to be threaded,
> but special interrupts can be excluded from this conversion.
> The cascade interrupt should be part of these exceptions.
> 
> In this case, irq2 is initialized before "kthreadd" task, which
> converts irq interrupt to threaded.
> 
> If this irq is threaded, the kernel calls "try_to_wake_up" function
> to wake up "kthreadd" task, but at that moment, "kthreadd" task
> has not been initialized and try_to_wake_up wakes up a NULL task.

That's not a reason to mark an interrupt NO_THREAD. The interrupt
handler could be non hardirq safe on RT. You'd run into other
problems.

In the case at hand it's the no_action handler which is hardirq safe
on RT and being no_action which means it simply returns IRQ_NONE.
I'll queue it for the next rt release and fixup the changelog myself.
 
Thanks,

	tglx


> Signed-off-by: Liming Wang <liming.wang@...driver.com>
> Signed-off-by: Bruce Ashfield <bruce.ashfield@...driver.com>
> ---
>  arch/mips/kernel/i8259.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/mips/kernel/i8259.c b/arch/mips/kernel/i8259.c
> index 5c74eb7..fb338db 100644
> --- a/arch/mips/kernel/i8259.c
> +++ b/arch/mips/kernel/i8259.c
> @@ -295,6 +295,7 @@ static void init_8259A(int auto_eoi)
>  static struct irqaction irq2 = {
>  	.handler = no_action,
>  	.name = "cascade",
> +	.flags = IRQF_NO_THREAD,
>  };
>  
>  static struct resource pic1_io_resource = {
> -- 
> 1.7.0.4
> 
> --
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