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

From: Palmer Dabbelt
Date: Tue Jun 25 2024 - 11:36:24 EST


On Sun, 09 Jun 2024 07:18:02 PDT (-0700), takakura@xxxxxxxxxxxxx wrote:
Hi Alex, Song,

On Fri, 24 May 2024, Alexandre Ghiti wrote:
Hi Song, Ryo,

On 06/05/2024 07:10, takakura@xxxxxxxxxxxxx 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