RE: [PATCH v4 2/2] kexec: Prevent redundant IRQ masking by checking state before shutdown

RE: [PATCH v4 2/2] kexec: Prevent redundant IRQ masking by checking state before shutdown

[Farber, Eliav]

On 11/29/2024 3:32 PM, Thomas Gleixner wrote:
>> This patch addresses the issue by:
>
> Again:  git grep 'This patch' Documentation/process/
Done (in v5 series)

[PATCH v4 0/2] Improve interrupt handling during machine kexec

[Eliav Farber]

This patch series focuses on improving the machine_kexec_mask_interrupts()
function by consolidating its implementation and optimizing its behavior to
avoid redundant interrupt masking.

Patch Summary:
[PATCH v4 1/2] Move machine_kexec_mask_interrupts() to kexec_core.c,
               removing duplicate architecture-specific implementations.
[PATCH v4 2/2] Refine machine_kexec_mask_interrupts() to avoid re-masking
               already-masked interrupts, resolving specific warnings
               triggered in GPIO IRQ flows.

Changes between v3 and v4:
 - Add missing <linux/irqdesc.h> and <linux/irq.h> includes.

Eliav Farber (2):
  kexec: Consolidate machine_kexec_mask_interrupts() implementation
  kexec: Prevent redundant IRQ masking by checking state before shutdown

 arch/arm/kernel/machine_kexec.c   | 23 -----------------------
 arch/arm64/kernel/machine_kexec.c | 31 -------------------------------
 arch/powerpc/include/asm/kexec.h  |  1 -
 arch/powerpc/kexec/core.c         | 22 ----------------------
 arch/riscv/kernel/machine_kexec.c | 23 -----------------------
 include/linux/irq.h               |  3 +++
 include/linux/kexec.h             |  2 ++
 kernel/irq/internals.h            |  1 -
 kernel/kexec_core.c               | 30 ++++++++++++++++++++++++++++++
 9 files changed, 35 insertions(+), 101 deletions(-)

-- 
2.40.1

[PATCH v4 2/2] kexec: Prevent redundant IRQ masking by checking state before shutdown

[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);
}
```

This issue surfaced after commit a8173820f441 ("gpio: gpiolib: Allow GPIO
IRQs to lazy disable") introduced lazy disablement for GPIO IRQs. It
replaced disable/enable hooks with mask/unmask hooks. Unlike the disable
hook, the mask hook doesn't handle already-masked IRQs.

When a GPIO-IRQ driver is unbound, the IRQ is released, triggering
__irq_disable() and irq_state_set_masked(). A subsequent call to
machine_kexec_mask_interrupts() re-invokes chip->irq_mask(). This results
in a call chain, including gpiochip_irq_mask() and gpiochip_disable_irq().
Since FLAG_USED_AS_IRQ was cleared earlier, a warning occurs.

This patch addresses the issue by:
 - Replacing the calls to irq_mask() and irq_disable() hooks with a
   simplified call to irq_shutdown().
 - Checking if the interrupt is started (irqd_is_started) before calling
   the shutdown.

As part of this change, the irq_shutdown() 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>
---
V4 -> V3: Add missing <linux/irq.h> include.

 include/linux/irq.h    | 3 +++
 kernel/irq/internals.h | 1 -
 kernel/kexec_core.c    | 9 +++------
 3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index fa711f80957b..48a3df728c47 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -694,6 +694,9 @@ extern int irq_chip_request_resources_parent(struct irq_data *data);
 extern void irq_chip_release_resources_parent(struct irq_data *data);
 #endif
 
+/* Shut down the interrupt */
+extern void irq_shutdown(struct irq_desc *desc);
+
 /* Handling of unhandled and spurious interrupts: */
 extern void note_interrupt(struct irq_desc *desc, irqreturn_t action_ret);
 
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index fe0272cd84a5..1f9287b1ccb7 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -88,7 +88,6 @@ extern int irq_activate(struct irq_desc *desc);
 extern int irq_activate_and_startup(struct irq_desc *desc, bool resend);
 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);
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 777191458544..09c8e9814cd2 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -41,6 +41,7 @@
 #include <linux/objtool.h>
 #include <linux/kmsg_dump.h>
 #include <linux/irqdesc.h>
+#include <linux/irq.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -1084,7 +1085,7 @@ void machine_kexec_mask_interrupts(void)
 		int check_eoi = 1;
 
 		chip = irq_desc_get_chip(desc);
-		if (!chip)
+		if (!chip || !irqd_is_started(&desc->irq_data))
 			continue;
 
 		if (IS_ENABLED(CONFIG_ARM64)) {
@@ -1098,10 +1099,6 @@ void machine_kexec_mask_interrupts(void)
 		if (check_eoi && 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_shutdown(desc);
 	}
 }
-- 
2.40.1

Re: [PATCH v4 2/2] kexec: Prevent redundant IRQ masking by checking state before shutdown

[Thomas Gleixner]

On Fri, Nov 29 2024 at 11:31, Eliav Farber wrote:
>
> This patch addresses the issue by:

Again:  git grep 'This patch' Documentation/process/