[-fixes] riscv: kexec: Avoid deadlock in kexec crash path

[Palmer Dabbelt]

On Sun, 09 Jun 2024 07:18:02 PDT (-0700), takakura at valinux.co.jp wrote:
> Hi Alex, Song,
>
> On Fri, 24 May 2024, Alexandre Ghiti wrote:
>>Hi Song, Ryo,
>>
>>On 06/05/2024 07:10, takakura at valinux.co.jp wrote:
>>> Hi Song and Paul!
>>>
>>>>> To avoid the deadlock, this patch directly EOI the irq regardless of
>>>>> the active status of irqchip.
>>>> Taking a quick look at the other architectures, looks like no one else is
>>>> doing this.  Is this addressing a RISC-V-only problem?
>>>>
>>>>> diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
>>>>> index f6c7135b00d7..d7ddf4d2b243 100644
>>>>> --- a/arch/riscv/kernel/machine_kexec.c
>>>>> +++ b/arch/riscv/kernel/machine_kexec.c
>>>>> @@ -149,20 +149,12 @@ static void machine_kexec_mask_interrupts(void)
>>>>>
>>>>>   	for_each_irq_desc(i, desc) {
>>>>>   		struct irq_chip *chip;
>>>>> -		int ret;
>>>>>
>>>>>   		chip = irq_desc_get_chip(desc);
>>>>>   		if (!chip)
>>>>>   			continue;
>>>>>
>>>>> -		/*
>>>>> -		 * First try to remove the active state. If this
>>>>> -		 * fails, try to EOI the interrupt.
>>>>> -		 */
>>>>> -		ret = irq_set_irqchip_state(i, IRQCHIP_STATE_ACTIVE, false);
>>>>> -
>>>>> -		if (ret && irqd_irq_inprogress(&desc->irq_data) &&
>>>>> -		    chip->irq_eoi)
>>>>> +		if (chip->irq_eoi && irqd_irq_inprogress(&desc->irq_data))
>>>>>   			chip->irq_eoi(&desc->irq_data);
>>> I think this deadlock is relevant to riscv and arm64 as they both
>>> acquire irqdesc spinlock by calling irq_set_irqchip_state() during their
>>> machine_kexec_mask_interrupts().
>>>
>>> However, I think calling irq_set_irqchip_state() during
>>> machine_kexec_mask_interrupts() is arm64 specific way of handling EOI
>>> which is not necessary for riscv.
>>> For arm64, its interrupt controller(gic) seems to have two ways of EOIing
>>> an interrupt depending on the mode which gic is configured. One of them
>>> treats EOI as two step procedure, priority drop and deactivation. I think
>>> irq_set_irqchip_state() is there to handle the deactivation part of
>>> the procedure.
>>> For riscv, EOI only requires irq_eoi handler to complete EOI and I think
>>> keeping irq_set_irqchip_state() will only leave this possible deadlock
>>> without any use.
>>> So I think it's best we simply remove irq_set_irqchip_state() as Song did.
>>
>>
>>I think this ^ is relevant and should be added to the commit log. @Song
>>can you respin another version with the updated commit log? @Ryo can you
>>add your Reviewed-by when it's done?
>
> Sure!

Just checking up on this one, I don't see a v2 on the lists.

>
>>This fix has been lagging behind for quite some time, it would be nice
>>to merge this in 6.10 and backport to stable.
>
> Sincerely,
>
> Ryo Takakura
>
>>Thanks,
>>
>>Alex