linux-kernel - Re: [PATCH RT 3/4] mips-remove-smp-reserve-lock.patch

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Date:	Thu, 07 Jun 2012 15:32:18 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	John Kacur <jkacur@...hat.com>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH RT 3/4] mips-remove-smp-reserve-lock.patch

On Thu, 2012-06-07 at 12:08 -0700, David Daney wrote:

> > Should it go to mainline stable?
> >
> 
> I don't think it is necessary.  As far as I know, RT may be the only 
> thing that needs it.

Ah, you're right. As this is just an issue because it is called with
interrupts disabled (from stop_machine). Although it's interesting that
the mips code, re-enables interrupts from that function.

>From kernel/cpu.c:

_cpu_down() {
	 __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));

take_cpu_down() {
	err = __cpu_disable();

kernel/stop_machine.c:

__stop_machine(int (*fn)(void *) ...) {
	local_irq_save(flags);
	hard_irq_disable();
	ret = (*fn)(data);
	local_irq_restore(flags);


arch/mips/include/asm/smp.h:

static inline int __cpu_disable(void)
{
        extern struct plat_smp_ops *mp_ops;     /* private */

        return mp_ops->cpu_disable();
}

arch/mips/cavium-octeon/smp.c:

octeon_cpu_disable(void) {
        local_irq_disable();
        fixup_irqs();
        local_irq_enable();

struct plat_smp_ops octeon_smp_ops = {
        .cpu_disable            = octeon_cpu_disable,


Is this expected? It causes the cpu notifiers to be called with
interrupts enabled. Not sure if that's a problem or not.

-- Steve


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