[ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Edgar Bonet]

Hello everybody!

I am facing an "Interrupts were enabled early" kernel warning which, as
far as I can tell, is caused by a spinlock guard in an ARM/Microchip
IRQCHIP driver. I think I solved the issue, and I am proposing a patch
below, after the scissor. But I must first disclose that:

  * I am completely new to Linux internals and its development process.
    This is why I chose to err on the side of providing too much
    information on my issue. It is not unlikely that I am doing
    something very wrong.

  * I am not subscribed to either of the linux-{,arm-}kernel mailing
    lists

  * I will be far from the Internet in the few days to come. I should be
    connected an responsive starting from 2025-08-24.


## Context

I am playing with an Acmesystems Acqua[1] system on module, which is
based on a SAMA5D31 SoC (single core Cortex-A5). I maintain the
Buildroot defconfig for this board,[2] which is currently based on a
vanilla Linux kernel v6.12.41.

As I wanted to check that the board runs fine on newer kernels, I built
a v6.16 for it using gcc 14, binutils 2.43, the in-tree sama5_defconfig
merged with this fragment:

    # CONFIG_BRIDGE is not set
    # CONFIG_MODULES is not set
    # CONFIG_NET_DSA is not set
    # CONFIG_WIRELESS is not set
    # CONFIG_USB_NET_DRIVERS is not set
    # CONFIG_WLAN is not set
    # CONFIG_MEDIA_SUPPORT is not set
    # CONFIG_SOUND is not set
    # CONFIG_AUTOFS_FS is not set

and the Buildroot-provided device tree, patched for compatibility with
Linux commit 510a6190cf5e ("ARM: dts: microchip: fix faulty ohci/ehci
node names").

The defconfig fragment above is meant to remove module support (with
some unused drivers along the way), which makes testing easier for me.


## Issue

While booting, Linux v6.16 printed this message on the serial console:

    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 0 at init/main.c:1024 start_kernel+0x4d0/0x5dc
    Interrupts were enabled early
    CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.16.0 #1 NONE 
    Hardware name: Atmel SAMA5
    Call trace: 
     unwind_backtrace from show_stack+0x10/0x14
     show_stack from dump_stack_lvl+0x38/0x48
     dump_stack_lvl from __warn+0x78/0xd4
     __warn from warn_slowpath_fmt+0x98/0xc8
     warn_slowpath_fmt from start_kernel+0x4d0/0x5dc
     start_kernel from 0x0
    ---[ end trace 0000000000000000 ]---

The board seemed to work fine, so maybe this warning is completely
harmless. It looked, however, scary enough to deserve some
investigation.


## Bug hunting

I could not reproduce the issue on a qemu virtual machine. All tests
were then done on the real hardware.

I looked for the Linux commit that introduced the issue. ‘git bisect’
told me this was 195298c3b116 ("genirq/generic-chip: Convert core code
to lock guards"). I then checked out a recent mainline kernel, namely
v6.17-rc1, and tried to revert that commit. For this, I first had to
revert two follow-up commits, namely 7ae844a6650c ("genirq/generic-chip:
Remove unused lock wrappers") and 771487050f83 ("genirq/generic-chip:
Fix incorrect lock guard conversions"). This was unsuccessful: I still
had the warning.

I went back to a clean v6.17-rc1 and tried to find the thing that was
enabling interrupts early. After lots of printk() debugging, I
discovered it was a guard(raw_spinlock_irq) destructor. The call chain
is this (line numbers are for v6.17-rc1):

    start_kernel (init/main.c:1011)
    -> time_init (arch/arm/kernel/time.c:96)
    -> timer_probe (drivers/clocksource/timer-probe.c:30)
    => tcb_clksrc_init (drivers/clocksource/timer-atmel-tcb.c:413)
    -> of_irq_get (drivers/of/irq.c:474)
    -> irq_create_of_mapping (kernel/irq/irqdomain.c:980)
    -> irq_create_fwspec_mapping (kernel/irq/irqdomain.c:848)
    => aic5_irq_domain_xlate (drivers/irqchip/irq-atmel-aic5.c:287)
    -> guard destructor (raw_spin_unlock_irq?)

where (=>) is an indirect call through a function pointer.


## Tentative fix

Commit 771487050f83 gave me the inspiration. The guard in question was
introduced by b00bee8afaca ("irqchip: Convert generic irqchip locking to
guards"), which replaced calls to irq_gc_lock_irq{save,restore}() by
guard(raw_spinlock_irq) (with no “save” in the name). The commit log
states that this is “intended and correct”, but I could not make sense
of the explanation. My (possibly faulty) understanding is that the guard
constructor disables interrupts, and the destructor either
unconditionally enables them (raw_spinlock_irq), or restores the
previous interrupt state (raw_spinlock_irqsave).

I then replaced guard(raw_spinlock_irq) with guard(raw_spinlock_irqsave)
and that seemed to do the job: the warning is gone. See the patch below
the scissors.

Best regards, and thank-you for reading so far.

Edgar Bonet.

[1] https://www.acmesystems.it/acqua
[2] https://gitlab.com/buildroot.org/buildroot/-/blob/2025.08-rc1/configs/acmesystems_acqua_a5_512mb_defconfig

------------------------------------------------------------------ >8 --
Subject: [PATCH] irqchip/atmel-aic5: Fix incorrect lock guard conversion

Commit b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
replaced calls to irq_gc_lock_irq{save,restore}() with
guard(raw_spinlock_irq). However, in irq-atmel-aic5.c, one such guard is
created early in the boot process, before interrupts are initially enabled.
As its destructor enables interrupts, this results in the following warning
on a SAMA5D31-based system:

    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 0 at init/main.c:1024 start_kernel+0x4d0/0x5dc
    Interrupts were enabled early
    CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.16.0 #1 NONE
    Hardware name: Atmel SAMA5
    Call trace:
     unwind_backtrace from show_stack+0x10/0x14
     show_stack from dump_stack_lvl+0x38/0x48
     dump_stack_lvl from __warn+0x78/0xd4
     __warn from warn_slowpath_fmt+0x98/0xc8
     warn_slowpath_fmt from start_kernel+0x4d0/0x5dc
     start_kernel from 0x0
    ---[ end trace 0000000000000000 ]---

Fix this by using guard(raw_spinlock_irqsave) instead.

Fixes: b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>
---
 drivers/irqchip/irq-atmel-aic5.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-atmel-aic5.c b/drivers/irqchip/irq-atmel-aic5.c
index 60b00d2c3d7a..1f14b401f71d 100644
--- a/drivers/irqchip/irq-atmel-aic5.c
+++ b/drivers/irqchip/irq-atmel-aic5.c
@@ -279,7 +279,7 @@ static int aic5_irq_domain_xlate(struct irq_domain *d,
 	if (ret)
 		return ret;
 
-	guard(raw_spinlock_irq)(&bgc->lock);
+	guard(raw_spinlock_irqsave)(&bgc->lock);
 	irq_reg_writel(bgc, *out_hwirq, AT91_AIC5_SSR);
 	smr = irq_reg_readl(bgc, AT91_AIC5_SMR);
 	aic_common_set_priority(intspec[2], &smr);
-- 
2.43.0

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Geert Uytterhoeven]

Hi Edgar,

CC loongson

On Thu, 14 Aug 2025 at 15:00, Edgar Bonet <bonet@grenoble.cnrs.fr> wrote:
> Subject: [PATCH] irqchip/atmel-aic5: Fix incorrect lock guard conversion
>
> Commit b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
> replaced calls to irq_gc_lock_irq{save,restore}() with
> guard(raw_spinlock_irq). However, in irq-atmel-aic5.c, one such guard is
> created early in the boot process, before interrupts are initially enabled.
> As its destructor enables interrupts, this results in the following warning
> on a SAMA5D31-based system:
>
>     ------------[ cut here ]------------
>     WARNING: CPU: 0 PID: 0 at init/main.c:1024 start_kernel+0x4d0/0x5dc
>     Interrupts were enabled early
>     CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.16.0 #1 NONE
>     Hardware name: Atmel SAMA5
>     Call trace:
>      unwind_backtrace from show_stack+0x10/0x14
>      show_stack from dump_stack_lvl+0x38/0x48
>      dump_stack_lvl from __warn+0x78/0xd4
>      __warn from warn_slowpath_fmt+0x98/0xc8
>      warn_slowpath_fmt from start_kernel+0x4d0/0x5dc
>      start_kernel from 0x0
>     ---[ end trace 0000000000000000 ]---
>
> Fix this by using guard(raw_spinlock_irqsave) instead.
>
> Fixes: b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
> Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

> --- a/drivers/irqchip/irq-atmel-aic5.c
> +++ b/drivers/irqchip/irq-atmel-aic5.c
> @@ -279,7 +279,7 @@ static int aic5_irq_domain_xlate(struct irq_domain *d,
>         if (ret)
>                 return ret;
>
> -       guard(raw_spinlock_irq)(&bgc->lock);
> +       guard(raw_spinlock_irqsave)(&bgc->lock);
>         irq_reg_writel(bgc, *out_hwirq, AT91_AIC5_SSR);
>         smr = irq_reg_readl(bgc, AT91_AIC5_SMR);
>         aic_common_set_priority(intspec[2], &smr);

I think the conversions in
drivers/irqchip/irq-atmel-aic.c:aic_irq_domain_xlate() and
drivers/irqchip/irq-loongson-liointc.c:liointc_set_type()
are also wrong, and need a similar change.
Unfortunately I have no hardware to verify.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Edgar Bonet]

Hello Geert, and thanks for you prompt review!

> I think the conversions in
> drivers/irqchip/irq-atmel-aic.c:aic_irq_domain_xlate() and
> drivers/irqchip/irq-loongson-liointc.c:liointc_set_type()
> are also wrong, and need a similar change.

The one in irq-atmel-aic.c looks indeed strikingly similar. The one in
irq-loongson-liointc.c is slightly different though. Instead of:

    irq_gc_lock_irqsave() -> guard(raw_spinlock_irq)

it does:

    irq_gc_lock_irqsave() -> guard(raw_spinlock)

I don't know what the implications are though.

> Unfortunately I have no hardware to verify.

Neither do I.

Regards,

Edgar.

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Thomas Gleixner]

On Thu, Aug 14 2025 at 17:28, Edgar Bonet wrote:
>> I think the conversions in
>> drivers/irqchip/irq-atmel-aic.c:aic_irq_domain_xlate() and
>> drivers/irqchip/irq-loongson-liointc.c:liointc_set_type()
>> are also wrong, and need a similar change.

> The one in irq-atmel-aic.c looks indeed strikingly similar.

Yes. My bad.

I missed the fact, that this can be invoked during early boot when
interrupts are still disabled. After early boot they are always enabled
when xlate() is invoked.

> The one in irq-loongson-liointc.c is slightly different
> though. Instead of:
>
>     irq_gc_lock_irqsave() -> guard(raw_spinlock_irq)
>
> it does:
>
>     irq_gc_lock_irqsave() -> guard(raw_spinlock)
>
> I don't know what the implications are though.

That's in the set_type() callback which is always invoked with the
interrupt decriptor lock held and interrupts disabled, so doing the
'save/restore' dance there is pointless.

Can you send a patch for that atmel-aic thing too please?

Thanks,

        tglx

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Thomas Gleixner]

On Sat, Aug 23 2025 at 21:33, Thomas Gleixner wrote:
> On Thu, Aug 14 2025 at 17:28, Edgar Bonet wrote:
>>> I think the conversions in
>>> drivers/irqchip/irq-atmel-aic.c:aic_irq_domain_xlate() and
>>> drivers/irqchip/irq-loongson-liointc.c:liointc_set_type()
>>> are also wrong, and need a similar change.
>
>> The one in irq-atmel-aic.c looks indeed strikingly similar.
>
> Yes. My bad.
>
> I missed the fact, that this can be invoked during early boot when
> interrupts are still disabled. After early boot they are always enabled
> when xlate() is invoked.
>
>> The one in irq-loongson-liointc.c is slightly different
>> though. Instead of:
>>
>>     irq_gc_lock_irqsave() -> guard(raw_spinlock_irq)
>>
>> it does:
>>
>>     irq_gc_lock_irqsave() -> guard(raw_spinlock)
>>
>> I don't know what the implications are though.
>
> That's in the set_type() callback which is always invoked with the
> interrupt decriptor lock held and interrupts disabled, so doing the
> 'save/restore' dance there is pointless.
>
> Can you send a patch for that atmel-aic thing too please?

Nah. Let me just fold it into your patch and be done with it.

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Nicolas Ferre]

On 14/08/2025 at 14:59, Edgar Bonet wrote:
> Hello everybody!
> 
> I am facing an "Interrupts were enabled early" kernel warning which, as
> far as I can tell, is caused by a spinlock guard in an ARM/Microchip
> IRQCHIP driver. I think I solved the issue, and I am proposing a patch
> below, after the scissor. But I must first disclose that:
> 
>    * I am completely new to Linux internals and its development process.
>      This is why I chose to err on the side of providing too much
>      information on my issue. It is not unlikely that I am doing
>      something very wrong.
> 
>    * I am not subscribed to either of the linux-{,arm-}kernel mailing
>      lists
> 
>    * I will be far from the Internet in the few days to come. I should be
>      connected an responsive starting from 2025-08-24.

Edgar,

Thanks a lot for having investigated this.


> ## Context
> 
> I am playing with an Acmesystems Acqua[1] system on module, which is
> based on a SAMA5D31 SoC (single core Cortex-A5). I maintain the
> Buildroot defconfig for this board,[2] which is currently based on a
> vanilla Linux kernel v6.12.41.
> 
> As I wanted to check that the board runs fine on newer kernels, I built
> a v6.16 for it using gcc 14, binutils 2.43, the in-tree sama5_defconfig
> merged with this fragment:
> 
>      # CONFIG_BRIDGE is not set
>      # CONFIG_MODULES is not set
>      # CONFIG_NET_DSA is not set
>      # CONFIG_WIRELESS is not set
>      # CONFIG_USB_NET_DRIVERS is not set
>      # CONFIG_WLAN is not set
>      # CONFIG_MEDIA_SUPPORT is not set
>      # CONFIG_SOUND is not set
>      # CONFIG_AUTOFS_FS is not set
> 
> and the Buildroot-provided device tree, patched for compatibility with
> Linux commit 510a6190cf5e ("ARM: dts: microchip: fix faulty ohci/ehci
> node names").
> 
> The defconfig fragment above is meant to remove module support (with
> some unused drivers along the way), which makes testing easier for me.
> 
> 
> ## Issue
> 
> While booting, Linux v6.16 printed this message on the serial console:
> 
>      ------------[ cut here ]------------
>      WARNING: CPU: 0 PID: 0 at init/main.c:1024 start_kernel+0x4d0/0x5dc
>      Interrupts were enabled early
>      CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.16.0 #1 NONE
>      Hardware name: Atmel SAMA5
>      Call trace:
>       unwind_backtrace from show_stack+0x10/0x14
>       show_stack from dump_stack_lvl+0x38/0x48
>       dump_stack_lvl from __warn+0x78/0xd4
>       __warn from warn_slowpath_fmt+0x98/0xc8
>       warn_slowpath_fmt from start_kernel+0x4d0/0x5dc
>       start_kernel from 0x0
>      ---[ end trace 0000000000000000 ]---

Indeed, reproduced on sam9x75 (which has AIC5), on 6.17.0-rc3.

> The board seemed to work fine, so maybe this warning is completely
> harmless. It looked, however, scary enough to deserve some
> investigation.
> 
> 
> ## Bug hunting
> 
> I could not reproduce the issue on a qemu virtual machine. All tests
> were then done on the real hardware.
> 
> I looked for the Linux commit that introduced the issue. ‘git bisect’
> told me this was 195298c3b116 ("genirq/generic-chip: Convert core code
> to lock guards"). I then checked out a recent mainline kernel, namely
> v6.17-rc1, and tried to revert that commit. For this, I first had to
> revert two follow-up commits, namely 7ae844a6650c ("genirq/generic-chip:
> Remove unused lock wrappers") and 771487050f83 ("genirq/generic-chip:
> Fix incorrect lock guard conversions"). This was unsuccessful: I still
> had the warning.
> 
> I went back to a clean v6.17-rc1 and tried to find the thing that was
> enabling interrupts early. After lots of printk() debugging, I
> discovered it was a guard(raw_spinlock_irq) destructor. The call chain
> is this (line numbers are for v6.17-rc1):
> 
>      start_kernel (init/main.c:1011)
>      -> time_init (arch/arm/kernel/time.c:96)
>      -> timer_probe (drivers/clocksource/timer-probe.c:30)
>      => tcb_clksrc_init (drivers/clocksource/timer-atmel-tcb.c:413)
>      -> of_irq_get (drivers/of/irq.c:474)
>      -> irq_create_of_mapping (kernel/irq/irqdomain.c:980)
>      -> irq_create_fwspec_mapping (kernel/irq/irqdomain.c:848)
>      => aic5_irq_domain_xlate (drivers/irqchip/irq-atmel-aic5.c:287)
>      -> guard destructor (raw_spin_unlock_irq?)
> 
> where (=>) is an indirect call through a function pointer.
> 
> 
> ## Tentative fix
> 
> Commit 771487050f83 gave me the inspiration. The guard in question was
> introduced by b00bee8afaca ("irqchip: Convert generic irqchip locking to
> guards"), which replaced calls to irq_gc_lock_irq{save,restore}() by
> guard(raw_spinlock_irq) (with no “save” in the name). The commit log
> states that this is “intended and correct”, but I could not make sense
> of the explanation. My (possibly faulty) understanding is that the guard
> constructor disables interrupts, and the destructor either
> unconditionally enables them (raw_spinlock_irq), or restores the
> previous interrupt state (raw_spinlock_irqsave).
> 
> I then replaced guard(raw_spinlock_irq) with guard(raw_spinlock_irqsave)
> and that seemed to do the job: the warning is gone. See the patch below
> the scissors.
> 
> Best regards, and thank-you for reading so far.
> 
> Edgar Bonet.
> 
> [1] https://www.acmesystems.it/acqua
> [2] https://gitlab.com/buildroot.org/buildroot/-/blob/2025.08-rc1/configs/acmesystems_acqua_a5_512mb_defconfig
> 
> ------------------------------------------------------------------ >8 --
> Subject: [PATCH] irqchip/atmel-aic5: Fix incorrect lock guard conversion
> 
> Commit b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
> replaced calls to irq_gc_lock_irq{save,restore}() with
> guard(raw_spinlock_irq). However, in irq-atmel-aic5.c, one such guard is
> created early in the boot process, before interrupts are initially enabled.
> As its destructor enables interrupts, this results in the following warning
> on a SAMA5D31-based system:
> 
>      ------------[ cut here ]------------
>      WARNING: CPU: 0 PID: 0 at init/main.c:1024 start_kernel+0x4d0/0x5dc
>      Interrupts were enabled early
>      CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.16.0 #1 NONE
>      Hardware name: Atmel SAMA5
>      Call trace:
>       unwind_backtrace from show_stack+0x10/0x14
>       show_stack from dump_stack_lvl+0x38/0x48
>       dump_stack_lvl from __warn+0x78/0xd4
>       __warn from warn_slowpath_fmt+0x98/0xc8
>       warn_slowpath_fmt from start_kernel+0x4d0/0x5dc
>       start_kernel from 0x0
>      ---[ end trace 0000000000000000 ]---
> 
> Fix this by using guard(raw_spinlock_irqsave) instead.
> 
> Fixes: b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
> Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>

Indeed. Thanks for the detailed explanation and the patch:

Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com> # on sam9x75
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com> (if needed)

Best regards,
   Nicolas

> ---
>   drivers/irqchip/irq-atmel-aic5.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-atmel-aic5.c b/drivers/irqchip/irq-atmel-aic5.c
> index 60b00d2c3d7a..1f14b401f71d 100644
> --- a/drivers/irqchip/irq-atmel-aic5.c
> +++ b/drivers/irqchip/irq-atmel-aic5.c
> @@ -279,7 +279,7 @@ static int aic5_irq_domain_xlate(struct irq_domain *d,
>          if (ret)
>                  return ret;
> 
> -       guard(raw_spinlock_irq)(&bgc->lock);
> +       guard(raw_spinlock_irqsave)(&bgc->lock);
>          irq_reg_writel(bgc, *out_hwirq, AT91_AIC5_SSR);
>          smr = irq_reg_readl(bgc, AT91_AIC5_SMR);
>          aic_common_set_priority(intspec[2], &smr);
> --
> 2.43.0

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Nicolas Ferre]

On 14/08/2025 at 17:28, Edgar Bonet wrote:
> Hello Geert, and thanks for you prompt review!

Yep, Geert, many thanks!

>> I think the conversions in
>> drivers/irqchip/irq-atmel-aic.c:aic_irq_domain_xlate() and
>> drivers/irqchip/irq-loongson-liointc.c:liointc_set_type()
>> are also wrong, and need a similar change.
> 
> The one in irq-atmel-aic.c looks indeed strikingly similar. The one in
> irq-loongson-liointc.c is slightly different though. Instead of:
> 
>      irq_gc_lock_irqsave() -> guard(raw_spinlock_irq)
> 
> it does:
> 
>      irq_gc_lock_irqsave() -> guard(raw_spinlock)
> 
> I don't know what the implications are though.
> 
>> Unfortunately I have no hardware to verify.
> 
> Neither do I.

I'm on it. Expect feedback later today...
Thanks so much for the heads-up.

Best regards,
   Nicolas

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Nicolas Ferre]

On 25/08/2025 at 14:35, Nicolas Ferre wrote:
> On 14/08/2025 at 17:28, Edgar Bonet wrote:
>> Hello Geert, and thanks for you prompt review!
> 
> Yep, Geert, many thanks!
> 
>>> I think the conversions in
>>> drivers/irqchip/irq-atmel-aic.c:aic_irq_domain_xlate() and
>>> drivers/irqchip/irq-loongson-liointc.c:liointc_set_type()
>>> are also wrong, and need a similar change.
>>
>> The one in irq-atmel-aic.c looks indeed strikingly similar. The one in
>> irq-loongson-liointc.c is slightly different though. Instead of:
>>
>>       irq_gc_lock_irqsave() -> guard(raw_spinlock_irq)
>>
>> it does:
>>
>>       irq_gc_lock_irqsave() -> guard(raw_spinlock)
>>
>> I don't know what the implications are though.
>>
>>> Unfortunately I have no hardware to verify.
>>
>> Neither do I.
> 
> I'm on it. Expect feedback later today...

Answering to myself: tested working okay on at91sam9x35ek board (with 
IRQ controller matching compatible string "atmel,at91rm9200-aic" 
(handled by file irq-atmel-aic.c) and your modification:

--- a/drivers/irqchip/irq-atmel-aic.c
+++ b/drivers/irqchip/irq-atmel-aic.c
@@ -188,7 +188,7 @@ static int aic_irq_domain_xlate(struct irq_domain *d,

         gc = dgc->gc[idx];

-       guard(raw_spinlock_irq)(&gc->lock);
+       guard(raw_spinlock_irqsave)(&gc->lock);
         smr = irq_reg_readl(gc, AT91_AIC_SMR(*out_hwirq));
         aic_common_set_priority(intspec[2], &smr);
         irq_reg_writel(gc, smr, AT91_AIC_SMR(*out_hwirq));

Thanks, best regards,
   Nicolas



> Thanks so much for the heads-up.
> 
> Best regards,
>     Nicolas
> 

Re: [ISSUE + PATCH] Interrupts were enabled early by spinlock guard

[Nicolas Ferre]

On 25/08/2025 at 14:33, Nicolas Ferre wrote:
> On 14/08/2025 at 14:59, Edgar Bonet wrote:
>> Hello everybody!
>>
>> I am facing an "Interrupts were enabled early" kernel warning which, as
>> far as I can tell, is caused by a spinlock guard in an ARM/Microchip
>> IRQCHIP driver. I think I solved the issue, and I am proposing a patch
>> below, after the scissor. But I must first disclose that:
>>
>>     * I am completely new to Linux internals and its development process.
>>       This is why I chose to err on the side of providing too much
>>       information on my issue. It is not unlikely that I am doing
>>       something very wrong.
>>
>>     * I am not subscribed to either of the linux-{,arm-}kernel mailing
>>       lists
>>
>>     * I will be far from the Internet in the few days to come. I should be
>>       connected an responsive starting from 2025-08-24.
> 
> Edgar,
> 
> Thanks a lot for having investigated this.
> 
> 
>> ## Context
>>
>> I am playing with an Acmesystems Acqua[1] system on module, which is
>> based on a SAMA5D31 SoC (single core Cortex-A5). I maintain the
>> Buildroot defconfig for this board,[2] which is currently based on a
>> vanilla Linux kernel v6.12.41.
>>
>> As I wanted to check that the board runs fine on newer kernels, I built
>> a v6.16 for it using gcc 14, binutils 2.43, the in-tree sama5_defconfig
>> merged with this fragment:
>>
>>       # CONFIG_BRIDGE is not set
>>       # CONFIG_MODULES is not set
>>       # CONFIG_NET_DSA is not set
>>       # CONFIG_WIRELESS is not set
>>       # CONFIG_USB_NET_DRIVERS is not set
>>       # CONFIG_WLAN is not set
>>       # CONFIG_MEDIA_SUPPORT is not set
>>       # CONFIG_SOUND is not set
>>       # CONFIG_AUTOFS_FS is not set
>>
>> and the Buildroot-provided device tree, patched for compatibility with
>> Linux commit 510a6190cf5e ("ARM: dts: microchip: fix faulty ohci/ehci
>> node names").
>>
>> The defconfig fragment above is meant to remove module support (with
>> some unused drivers along the way), which makes testing easier for me.
>>
>>
>> ## Issue
>>
>> While booting, Linux v6.16 printed this message on the serial console:
>>
>>       ------------[ cut here ]------------
>>       WARNING: CPU: 0 PID: 0 at init/main.c:1024 start_kernel+0x4d0/0x5dc
>>       Interrupts were enabled early
>>       CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.16.0 #1 NONE
>>       Hardware name: Atmel SAMA5
>>       Call trace:
>>        unwind_backtrace from show_stack+0x10/0x14
>>        show_stack from dump_stack_lvl+0x38/0x48
>>        dump_stack_lvl from __warn+0x78/0xd4
>>        __warn from warn_slowpath_fmt+0x98/0xc8
>>        warn_slowpath_fmt from start_kernel+0x4d0/0x5dc
>>        start_kernel from 0x0
>>       ---[ end trace 0000000000000000 ]---
> 
> Indeed, reproduced on sam9x75 (which has AIC5), on 6.17.0-rc3.
> 
>> The board seemed to work fine, so maybe this warning is completely
>> harmless. It looked, however, scary enough to deserve some
>> investigation.
>>
>>
>> ## Bug hunting
>>
>> I could not reproduce the issue on a qemu virtual machine. All tests
>> were then done on the real hardware.
>>
>> I looked for the Linux commit that introduced the issue. ‘git bisect’
>> told me this was 195298c3b116 ("genirq/generic-chip: Convert core code
>> to lock guards"). I then checked out a recent mainline kernel, namely
>> v6.17-rc1, and tried to revert that commit. For this, I first had to
>> revert two follow-up commits, namely 7ae844a6650c ("genirq/generic-chip:
>> Remove unused lock wrappers") and 771487050f83 ("genirq/generic-chip:
>> Fix incorrect lock guard conversions"). This was unsuccessful: I still
>> had the warning.
>>
>> I went back to a clean v6.17-rc1 and tried to find the thing that was
>> enabling interrupts early. After lots of printk() debugging, I
>> discovered it was a guard(raw_spinlock_irq) destructor. The call chain
>> is this (line numbers are for v6.17-rc1):
>>
>>       start_kernel (init/main.c:1011)
>>       -> time_init (arch/arm/kernel/time.c:96)
>>       -> timer_probe (drivers/clocksource/timer-probe.c:30)
>>       => tcb_clksrc_init (drivers/clocksource/timer-atmel-tcb.c:413)
>>       -> of_irq_get (drivers/of/irq.c:474)
>>       -> irq_create_of_mapping (kernel/irq/irqdomain.c:980)
>>       -> irq_create_fwspec_mapping (kernel/irq/irqdomain.c:848)
>>       => aic5_irq_domain_xlate (drivers/irqchip/irq-atmel-aic5.c:287)
>>       -> guard destructor (raw_spin_unlock_irq?)
>>
>> where (=>) is an indirect call through a function pointer.
>>
>>
>> ## Tentative fix
>>
>> Commit 771487050f83 gave me the inspiration. The guard in question was
>> introduced by b00bee8afaca ("irqchip: Convert generic irqchip locking to
>> guards"), which replaced calls to irq_gc_lock_irq{save,restore}() by
>> guard(raw_spinlock_irq) (with no “save” in the name). The commit log
>> states that this is “intended and correct”, but I could not make sense
>> of the explanation. My (possibly faulty) understanding is that the guard
>> constructor disables interrupts, and the destructor either
>> unconditionally enables them (raw_spinlock_irq), or restores the
>> previous interrupt state (raw_spinlock_irqsave).
>>
>> I then replaced guard(raw_spinlock_irq) with guard(raw_spinlock_irqsave)
>> and that seemed to do the job: the warning is gone. See the patch below
>> the scissors.
>>
>> Best regards, and thank-you for reading so far.
>>
>> Edgar Bonet.
>>
>> [1] https://www.acmesystems.it/acqua
>> [2] https://gitlab.com/buildroot.org/buildroot/-/blob/2025.08-rc1/configs/acmesystems_acqua_a5_512mb_defconfig
>>
>> ------------------------------------------------------------------ >8 --
>> Subject: [PATCH] irqchip/atmel-aic5: Fix incorrect lock guard conversion
>>
>> Commit b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
>> replaced calls to irq_gc_lock_irq{save,restore}() with
>> guard(raw_spinlock_irq). However, in irq-atmel-aic5.c, one such guard is
>> created early in the boot process, before interrupts are initially enabled.
>> As its destructor enables interrupts, this results in the following warning
>> on a SAMA5D31-based system:
>>
>>       ------------[ cut here ]------------
>>       WARNING: CPU: 0 PID: 0 at init/main.c:1024 start_kernel+0x4d0/0x5dc
>>       Interrupts were enabled early
>>       CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.16.0 #1 NONE
>>       Hardware name: Atmel SAMA5
>>       Call trace:
>>        unwind_backtrace from show_stack+0x10/0x14
>>        show_stack from dump_stack_lvl+0x38/0x48
>>        dump_stack_lvl from __warn+0x78/0xd4
>>        __warn from warn_slowpath_fmt+0x98/0xc8
>>        warn_slowpath_fmt from start_kernel+0x4d0/0x5dc
>>        start_kernel from 0x0
>>       ---[ end trace 0000000000000000 ]---
>>
>> Fix this by using guard(raw_spinlock_irqsave) instead.
>>
>> Fixes: b00bee8afaca ("irqchip: Convert generic irqchip locking to guards")
>> Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>
> 
> Indeed. Thanks for the detailed explanation and the patch:
> 
> Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com> # on sam9x75

For you Thomas, also this test:
Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com> # on sam9x35 (for 
similar changes to irq-atmel-aic.c)

Thanks, best regards,
   Nicolas


> Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com> (if needed)
> 
> Best regards,
>     Nicolas
> 
>> ---
>>    drivers/irqchip/irq-atmel-aic5.c | 2 +-
>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-atmel-aic5.c b/drivers/irqchip/irq-atmel-aic5.c
>> index 60b00d2c3d7a..1f14b401f71d 100644
>> --- a/drivers/irqchip/irq-atmel-aic5.c
>> +++ b/drivers/irqchip/irq-atmel-aic5.c
>> @@ -279,7 +279,7 @@ static int aic5_irq_domain_xlate(struct irq_domain *d,
>>           if (ret)
>>                   return ret;
>>
>> -       guard(raw_spinlock_irq)(&bgc->lock);
>> +       guard(raw_spinlock_irqsave)(&bgc->lock);
>>           irq_reg_writel(bgc, *out_hwirq, AT91_AIC5_SSR);
>>           smr = irq_reg_readl(bgc, AT91_AIC5_SMR);
>>           aic_common_set_priority(intspec[2], &smr);
>> --
>> 2.43.0
>