linux-kernel - [PATCH] arm64: kexec: Check if IRQ is already masked before masking

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Message-ID: <20241126050509.4426-1-farbere@amazon.com>
Date: Tue, 26 Nov 2024 05:05:09 +0000
From: Eliav Farber <farbere@...zon.com>
To: <catalin.marinas@....com>, <will@...nel.org>, <akpm@...ux-foundation.org>,
	<bhe@...hat.com>, <farbere@...zon.com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
CC: <jonnyc@...zon.com>
Subject: [PATCH] arm64: kexec: Check if IRQ is already masked before masking

During machine kexec, the function machine_kexec_mask_interrupts() is
responsible for masking all interrupts. However, the current
implementation unconditionally calls the irq_mask() function for each
interrupt descriptor, even if the interrupt is already masked.

This commit adds a check to verify if the interrupt is not already
masked before calling the irq_mask() function. This change avoids
redundant masking operations and potential issues that might arise from
attempting to mask an already masked interrupt.

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);
}
```

This issue began after commit a8173820f441 ("gpio: gpiolib: Allow GPIO
IRQs to lazy disable"), which replaced IRQ disable/enable hooks with
mask/unmask hooks in some cases. The irq_disable hook was protected
against disabling an already disabled IRQ, but the irq_mask hook in
machine_kexec_mask_interrupts() was not.

When a driver that uses a GPIO-irq is unbound, the corresponding IRQ is
released, invoking __irq_disable() and irq_state_set_masked().
Subsequently, machine_kexec_mask_interrupts() attempts to call the
chip->irq_mask() function again. This invokes gpiochip_irq_mask() and
gpiochip_disable_irq(), and since FLAG_USED_AS_IRQ has already been
cleared, this results in a warning being printed.

Signed-off-by: Eliav Farber <farbere@...zon.com>
---
 arch/arm64/kernel/machine_kexec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index 82e2203d86a3..6f56ec676844 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -230,7 +230,7 @@ static void machine_kexec_mask_interrupts(void)
 		    chip->irq_eoi)
 			chip->irq_eoi(&desc->irq_data);

-		if (chip->irq_mask)
+		if (chip->irq_mask && !irqd_irq_masked(&desc->irq_data))
 			chip->irq_mask(&desc->irq_data);

 		if (chip->irq_disable && !irqd_irq_disabled(&desc->irq_data))
-- 
2.40.1