Re: [PATCH] irqchip/jcore-aic: Fix lost IPIs on SMP

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

Hi Karl,

On Mon, 2026-09-28 at 05:54 +0200, Karl Mehltretter wrote:
> Since commit bdf4e2ac295fe ("genirq: Allow per-cpu interrupt sharing for
> non-overlapping affinities"), handle_percpu_devid_irq() only runs an
> action whose affinity mask contains the current CPU. Only actions set up
> through the percpu_devid request functions have such a mask.
> 
> handle_jcore_irq() passes every per-CPU interrupt to
> handle_percpu_devid_irq(). The J2 IPI is not a percpu_devid interrupt.
> j2_prepare_cpus() requests it with request_irq() and IRQF_PERCPU, so its
> action has no affinity mask and cpumask_test_cpu() reads through a NULL
> pointer. J2 has no MMU to catch this. The read returns whatever is at
> address 0, the action is not found, and IPIs are dropped as spurious
> ("Spurious percpu IRQ20 on CPU1", printed once).
> 
> Pass only percpu_devid interrupts (the PIT) to handle_percpu_devid_irq()
> and the other per-CPU interrupts to handle_percpu_irq() again, as before
> commit d7e3fd658248f ("irqchip/jcore-aic, clocksource/drivers/jcore: Fix
> jcore-pit interrupt request").
> 
> Found with a two-CPU J2 model simulated from the J-Core RTL. Without
> this change the boot stalls with both CPUs idle shortly after
> "smp: Brought up 1 node, 2 CPUs". With it, the boot reaches userspace.
> 
> Fixes: bdf4e2ac295fe ("genirq: Allow per-cpu interrupt sharing for non-overlapping affinities")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
> ---
> 
> Notes:
>     Tested on a two-CPU J2 model simulated from the J-Core RTL with
>     Verilator (J2 CPUs, caches, bus mux and AIC1 from jcore-cpu/jcore-soc),
>     kernel v7.3-rc4 j2_defconfig with SMP=y:
>     
>     - unpatched: "Spurious percpu IRQ20 on CPU1", pending IPI messages are
>       never cleared (the message word of CPU1 grows to 0x6), boot stalls
>       with both CPUs idle after SMP bring-up
>     - patched: IPIs are handled, boot reaches userspace on both CPUs
>     
>     Not tested on J-Core hardware. Testing on real hardware is welcome.
> 
>  drivers/irqchip/irq-jcore-aic.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-jcore-aic.c b/drivers/irqchip/irq-jcore-aic.c
> index 94c05cf974be8..b4fee02997eee 100644
> --- a/drivers/irqchip/irq-jcore-aic.c
> +++ b/drivers/irqchip/irq-jcore-aic.c
> @@ -37,8 +37,10 @@ static struct irq_chip jcore_aic;
>  
>  static void handle_jcore_irq(struct irq_desc *desc)
>  {
> -	if (irqd_is_per_cpu(irq_desc_get_irq_data(desc)))
> +	if (irq_is_percpu_devid(irq_desc_get_irq(desc)))
>  		handle_percpu_devid_irq(desc);
> +	else if (irqd_is_per_cpu(irq_desc_get_irq_data(desc)))
> +		handle_percpu_irq(desc);
>  	else
>  		handle_simple_irq(desc);
>  }

Can you tell me what toolchain you used to build the kernel for J2?

Last time I tried to use the one provided by Rob Landley, the build
failed due to an internal compiler error so I couldn't actually build
a kernel to test it on my J2 Turtleboard.

Adrian

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