linux-kernel - Re: [v2 2/5] arm64: kdump: implement machine_crash

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Message-ID: <55C3083D.1000306@linaro.org>
Date:	Thu, 06 Aug 2015 16:09:49 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>,
	Mark Rutland <mark.rutland@....com>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>,
	"hbabus@...ibm.com" <hbabus@...ibm.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"geoff@...radead.org" <geoff@...radead.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"david.griego@...aro.org" <david.griego@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v2 2/5] arm64: kdump: implement machine_crash_shutdown()

Marc, Mark

Sorry for not revisiting your comment below for a while.

On 04/24/2015 07:43 PM, Marc Zyngier wrote:
> On 24/04/15 11:39, Mark Rutland wrote:
>> On Fri, Apr 24, 2015 at 08:53:05AM +0100, AKASHI Takahiro wrote:
>>> kdump calls machine_crash_shutdown() to shut down non-boot cpus and
>>> save per-cpu general-purpose registers before restarting the crash dump
>>> kernel. See kernel_kexec().
>>> ipi_cpu_stop() is used and a bit modified to support this behavior.
>>>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
>>> ---
>>>   arch/arm64/include/asm/kexec.h    |   34 ++++++++++++++++++++++-
>>>   arch/arm64/kernel/machine_kexec.c |   55 ++++++++++++++++++++++++++++++++++++-
>>>   arch/arm64/kernel/smp.c           |   12 ++++++--
>>>   3 files changed, 97 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
>>> index 3530ff5..eaf3fcb 100644
>>> --- a/arch/arm64/include/asm/kexec.h
>>> +++ b/arch/arm64/include/asm/kexec.h
>>> @@ -30,6 +30,8 @@
>>>
>>>   #if !defined(__ASSEMBLY__)
>>>
>>> +extern bool in_crash_kexec;
>>> +
>>>   /**
>>>    * crash_setup_regs() - save registers for the panic kernel
>>>    *
>>> @@ -40,7 +42,37 @@
>>>   static inline void crash_setup_regs(struct pt_regs *newregs,
>>>   				    struct pt_regs *oldregs)
>>>   {
>>> -	/* Empty routine needed to avoid build errors. */
>>> +	if (oldregs) {
>>> +		memcpy(newregs, oldregs, sizeof(*newregs));
>>> +	} else {
>>> +		__asm__ __volatile__ (
>>> +			"stp	 x0,   x1, [%3]\n\t"
>>
>> Why the tabs?
>>
>> Please use #16 * N as the offset for consistency with entry.S, with 0
>> for the first N.
>>
>> [...]
>>
>>> +static void machine_kexec_mask_interrupts(void)
>>> +{
>>> +	unsigned int i;
>>> +	struct irq_desc *desc;
>>> +
>>> +	for_each_irq_desc(i, desc) {
>>> +		struct irq_chip *chip;
>>> +
>>> +		chip = irq_desc_get_chip(desc);
>>> +		if (!chip)
>>> +			continue;
>>> +
>>> +		if (chip->irq_eoi && irqd_irq_inprogress(&desc->irq_data))
>>> +			chip->irq_eoi(&desc->irq_data);
>>> +
>>> +		if (chip->irq_mask)
>>> +			chip->irq_mask(&desc->irq_data);
>>> +
>>> +		if (chip->irq_disable && !irqd_irq_disabled(&desc->irq_data))
>>> +			chip->irq_disable(&desc->irq_data);
>>> +	}
>>> +}
>>
>> I'm surprised that this isn't left to the irqchip driver init code in
>> the crash kernel. For all we know this state could be corrupt anyway.
>
> Indeed, parsing the irqdesc list is a recipe for disaster. Who knows
> which locks have been taken or simply corrupted, pointers nuked...
>
>> Is there any reason we can't get the GIC driver to nuke all of this at
>> probe time?

Is it just enough to remove kexec_mask_interrupts() and add gic_eoi_irq()
at the beginning of gic_cpu_init() in irq-gic.c and irq-gic-v3.c?

> This feels like the better option. I can cook a patch or two for that.

If you do, that will be much better :)

BTW, in arm-gic-v3.h, GICD_CTRL_ARE_NS is defined as
     (1U << 4)
but should it be 5?
(I'm referring to the page 8-415 in IHI0069A.)

Thanks,
-Takahiro AKASHI

> Thanks,
>
> 	M.
>
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