linux-kernel - Re: Possible race in request_irq() (__setup

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Date:	Fri, 25 May 2012 16:01:29 +0200
From:	Alexander Sverdlin <asv@...go.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	David Daney <ddaney@...iumnetworks.com>,
	Venkat Subbiah <venkat.subbiah@...ium.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Possible race in request_irq() (__setup_irq())

Hello Thomas, David, Venkat,

On 05/16/2012 03:44 PM, Thomas Gleixner wrote:
> Your irq is using handle_percpu_irq() as the flow handler.
> 
> handle_percpu_irq() is a special flow handler which does not take the
> irq descriptor lock for performance reasons. It's a single interrupt
> number which has a percpu dev_id and can be handled on all cores in
> parallel.
> 
> The interrupts need to be marked as such and requested with
> request_percpu_irq(). Those interrupts are either marked as
> NOAUTOENABLE or set up by the low level setup code, which runs on the
> boot cpu with interrupt enabled.
> 
> Those interrupts are marked as percpu and can only be requested with
> request_percpu_irq().
> 

Could someone comment please, why exactly this happens in current linux-next for Octeon:

In arch/mips/cavium-octeon/octeon-irq.c MBOX IRQs are set up to be handled by handle_percpu_irq():

static void __init octeon_irq_init_ciu(void)
{
...
	octeon_irq_set_ciu_mapping(OCTEON_IRQ_MBOX0, 0, 32, chip_mbox, handle_percpu_irq);
	octeon_irq_set_ciu_mapping(OCTEON_IRQ_MBOX1, 0, 33, chip_mbox, handle_percpu_irq);

But in arch/mips/cavium-octeon/smp.c it's requested as normal IRQ:

void octeon_prepare_cpus(unsigned int max_cpus)
{
...
	if (request_irq(OCTEON_IRQ_MBOX0, mailbox_interrupt,
			IRQF_PERCPU | IRQF_NO_THREAD, "SMP-IPI",
			mailbox_interrupt)) {
		panic("Cannot request_irq(OCTEON_IRQ_MBOX0)");
	}

Is it a bug, or some kind of special case?

-- 
Best regards,
Alexander Sverdlin.
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