If the kexec crash code is called in the interrupt context, the
machine_kexec_mask_interrupts() function will trigger a deadlock while
trying to acquire the irqdesc spinlock and then deacitive irqchip.
To avoid the deadlock, this patch directly EOI the irq regardless of
the active status of irqchip.
Fixes: b17d19a5314a ("riscv: kexec: Fixup irq controller broken in kexec crash path")
Signed-off-by: Song Shuai <[email protected]>
---
Note that:
1. this deadlock can reproduced via echo EXCEPTION to lkdtm INT_HW_IRQ_EN point
2. RISC-V HLIC and PLIC irqchips don't have the irq_set_irqchip_state handler
and I don't know is it ok to deactive irqchip without the spinlock in this
code context, so I simply removed that snippet as arm and powerpc do.
I would like to listen to your advice.
---
arch/riscv/kernel/machine_kexec.c | 10 +---------
1 file changed, 1 insertion(+), 9 deletions(-)
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);
if (chip->irq_mask)
--
2.20.1
Hi Song Shuai,
On Fri, 8 Dec 2023, Song Shuai wrote:
> If the kexec crash code is called in the interrupt context, the
> machine_kexec_mask_interrupts() function will trigger a deadlock while
> trying to acquire the irqdesc spinlock and then deacitive irqchip.
>
> 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);
- Paul
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.
Sincerely,
Ryo Takakura