[PATCH v2] arm64: kexec: Check if IRQ is already masked before masking

[PATCH v2] arm64: kexec: Check if IRQ is already masked before masking

[Eliav Farber]

During machine kexec, the function machine_kexec_mask_interrupts() is
responsible for disabling or masking all interrupts. While the
irq_disable hook ensures that an already-disabled IRQ is not disabled
again, the current implementation unconditionally invokes the irq_mask()
function for every interrupt descriptor, even when the interrupt is
already masked.

A specific issue was observed in the crash kernel flow after unbinding a
device (prior to kexec) that used a GPIO as an IRQ source. The warning
was triggered by the gpiochip_disable_irq() function, which attempted to
clear the FLAG_IRQ_IS_ENABLED flag when FLAG_USED_AS_IRQ was not set:

```
void gpiochip_disable_irq(struct gpio_chip *gc, unsigned int offset)
{
	struct gpio_desc *desc = gpiochip_get_desc(gc, offset);

	if (!IS_ERR(desc) &&
	    !WARN_ON(!test_bit(FLAG_USED_AS_IRQ, &desc->flags)))
		clear_bit(FLAG_IRQ_IS_ENABLED, &desc->flags);
}
```

The issue emerged after commit a8173820f441 ("gpio: gpiolib: Allow GPIO
IRQs to lazy disable"), which introduced lazy disablement for GPIO IRQs
by replacing disable/enable hooks with mask/unmask hooks in some cases.
While irq_disable guarded against redundant operations, the unguarded
irq_mask in machine_kexec_mask_interrupts() led to warnings when invoked
on already-masked IRQs.

When a GPIO-IRQ-using driver is unbound, the IRQ is released, invoking
__irq_disable() and irq_state_set_masked(). A subsequent call to
machine_kexec_mask_interrupts() reinvoked chip->irq_mask(), leading to a
call chain that included gpiochip_irq_mask() and gpiochip_disable_irq().
Because FLAG_USED_AS_IRQ was cleared earlier, a warning was printed.

This patch replaces the direct invocation of the irq_mask() and
irq_disable() hooks with simplified code that leverages the
irq_disable() kernel infrastructure. This higher-level function checks
the interrupt's state to prevent redundant operations. Additionally, the
IRQ_DISABLE_UNLAZY status flag is set to ensure that, for interrupt
chips lacking an irq_disable callback, the disable operation is handled
using the lazy approach.

As part of this change, the irq_disable() declaration was moved from
kernel/irq/internals.h to include/linux/irq.h to make it accessible
outside the kernel/irq/ directory, as the former can only be included
within that directory.

Signed-off-by: Eliav Farber <farbere@amazon.com>
---
V1 -> V2:
- Implement an alternative solution by utilizing the kernel's
  irq_disable() infrastructure.
- Apply the fix to additional architectures, including ARM, PowerPC,
  and RISC-V.
---
 arch/arm/kernel/machine_kexec.c   | 7 ++-----
 arch/arm64/kernel/machine_kexec.c | 7 ++-----
 arch/powerpc/kexec/core.c         | 7 ++-----
 arch/riscv/kernel/machine_kexec.c | 7 ++-----
 include/linux/irq.h               | 2 ++
 kernel/irq/internals.h            | 1 -
 6 files changed, 10 insertions(+), 21 deletions(-)

diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index 80ceb5bd2680..54d0bd1bd449 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -142,11 +142,8 @@ static void machine_kexec_mask_interrupts(void)
 		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);
+		irq_set_status_flags(i, IRQ_DISABLE_UNLAZY);
+		irq_disable(desc);
 	}
 }
 
diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index 82e2203d86a3..9b48d952df3e 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -230,11 +230,8 @@ static void machine_kexec_mask_interrupts(void)
 		    chip->irq_eoi)
 			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);
+		irq_set_status_flags(i, IRQ_DISABLE_UNLAZY);
+		irq_disable(desc);
 	}
 }
 
diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
index b8333a49ea5d..3489e50f5017 100644
--- a/arch/powerpc/kexec/core.c
+++ b/arch/powerpc/kexec/core.c
@@ -36,11 +36,8 @@ void machine_kexec_mask_interrupts(void) {
 		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);
+		irq_set_status_flags(i, IRQ_DISABLE_UNLAZY);
+		irq_disable(desc);
 	}
 }
 
diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
index 3c830a6f7ef4..a9df80e0602c 100644
--- a/arch/riscv/kernel/machine_kexec.c
+++ b/arch/riscv/kernel/machine_kexec.c
@@ -129,11 +129,8 @@ static void machine_kexec_mask_interrupts(void)
 		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);
+		irq_set_status_flags(i, IRQ_DISABLE_UNLAZY);
+		irq_disable(desc);
 	}
 }
 
diff --git a/include/linux/irq.h b/include/linux/irq.h
index fa711f80957b..176a7f671409 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -600,6 +600,8 @@ enum {
 
 #define IRQ_DEFAULT_INIT_FLAGS	ARCH_IRQ_INIT_FLAGS
 
+extern void irq_disable(struct irq_desc *desc);
+
 struct irqaction;
 extern int setup_percpu_irq(unsigned int irq, struct irqaction *new);
 extern void remove_percpu_irq(unsigned int irq, struct irqaction *act);
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index fe0272cd84a5..d9104d2b26b4 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -91,7 +91,6 @@ extern int irq_startup(struct irq_desc *desc, bool resend, bool force);
 extern void irq_shutdown(struct irq_desc *desc);
 extern void irq_shutdown_and_deactivate(struct irq_desc *desc);
 extern void irq_enable(struct irq_desc *desc);
-extern void irq_disable(struct irq_desc *desc);
 extern void irq_percpu_enable(struct irq_desc *desc, unsigned int cpu);
 extern void irq_percpu_disable(struct irq_desc *desc, unsigned int cpu);
 extern void mask_irq(struct irq_desc *desc);
-- 
2.40.1


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Re: [PATCH v2] arm64: kexec: Check if IRQ is already masked before masking

[Thomas Gleixner]

On Wed, Nov 27 2024 at 15:22, Eliav Farber wrote:
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
> index 80ceb5bd2680..54d0bd1bd449 100644
> --- a/arch/arm/kernel/machine_kexec.c
> +++ b/arch/arm/kernel/machine_kexec.c
> @@ -142,11 +142,8 @@ static void machine_kexec_mask_interrupts(void)
>  		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);
> +		irq_set_status_flags(i, IRQ_DISABLE_UNLAZY);
> +		irq_disable(desc);

This is just wrong. If the interrupt was torn down, then its state is
deactivated and it was masked already. So the EOI handling and the
mask/disable dance are neither required nor make sense.

So this whole thing should be:

		chip = irq_desc_get_chip(desc);
-		if (!chip)
+		if (!chip || !irqd_is_started(&desc->irq_data))
                	continue;

But what's worse is that we have 4 almost identical variants of the same
code.

So instead of exposing core functionality and "fixing" up four variants,
can we please have a consolidated version of this function in the core
code:
                struct irq_chip *chip;
                int check_eoi = 1;

		chip = irq_desc_get_chip(desc);
		if (!chip || !irqd_is_started(&desc->irq_data))
                	continue;

                if (IS_ENABLED(CONFIG_.....)) {
                        /*
                         * Add a sensible comment which explains this.
                         */
                	check_eoi = irq_set_irqchip_state(....);
                }

		if (check_eoi && ....)
                	chip->irq_eoi(&desc->irq_data);

		irq_shutdown(desc);

No?

Thanks,

        tglx

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Re: [PATCH v2] arm64: kexec: Check if IRQ is already masked before masking

[Thomas Gleixner]

On Wed, Nov 27 2024 at 15:22, Eliav Farber wrote:

As a related note. The subject line is not really matching what the
patch does. It want's to be split into a core change and one patch per
architecture.

> This patch replaces the direct invocation of the irq_mask() and

git grep 'This patch' Documentation/process/

> irq_disable() hooks with simplified code that leverages the
> irq_disable() kernel infrastructure. This higher-level function checks
> the interrupt's state to prevent redundant operations. Additionally, the
> IRQ_DISABLE_UNLAZY status flag is set to ensure that, for interrupt
> chips lacking an irq_disable callback, the disable operation is handled
> using the lazy approach.

Not that it matters much anymore, but the last sentence does not make
sense:

  Set the UNLAZY flag so disable is handled using the LAZY approach ...

Thanks,

        tglx

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RE: [PATCH v2] arm64: kexec: Check if IRQ is already masked before masking

[Farber, Eliav]

On 11/28/2024 12:39 PM, Thomas Gleixner wrote:
> This is just wrong. If the interrupt was torn down, then its state is deactivated and it was masked already. So the EOI handling and the mask/disable dance are neither required nor make sense.
>
> So this whole thing should be:
>
>                 chip = irq_desc_get_chip(desc);
> -               if (!chip)
> +               if (!chip || !irqd_is_started(&desc->irq_data))
>                         continue;
ACK. Will be done this way in V3.

> But what's worse is that we have 4 almost identical variants of the same code.
>
> So instead of exposing core functionality and "fixing" up four variants, can we please have a consolidated version of this function in the core
> code:
>                 struct irq_chip *chip;
>                 int check_eoi = 1;
>
>                 chip = irq_desc_get_chip(desc);
>                 if (!chip || !irqd_is_started(&desc->irq_data))
>                         continue;
>
>                 if (IS_ENABLED(CONFIG_.....)) {
>                         /*
>                          * Add a sensible comment which explains this.
>                          */
>                         check_eoi = irq_set_irqchip_state(....);
>                 }
>
>                 if (check_eoi && ....)
>                         chip->irq_eoi(&desc->irq_data);
>
>                 irq_shutdown(desc);
>
> No?
In V3 I will add a preliminary patch that will remove the four variants
and instead add a common implementations to the kexec core.

Thanks, Eliav

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