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Message-ID: <4FD10547.9080804@gmail.com>
Date: Thu, 07 Jun 2012 12:47:19 -0700
From: David Daney <ddaney.cavm@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Ralf Baechle <ralf@...ux-mips.org>
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>
Subject: Re: [PATCH RT 3/4] mips-remove-smp-reserve-lock.patch
On 06/07/2012 12:32 PM, Steven Rostedt wrote:
> 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.
I am inclined to go with your instinct here. Probably we shouldn't
unconditionally local_irq_enable() here.
Perhaps {,raw}_local_irq_save/{,raw}local_irq_restore would be better.
Or even no local irq enable manipulation...
In any event, I may let Ralf sort it out.
David Daney
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