Re: [PATCH] genirq/msi: Shutdown managed interrupts with unsatifiable affinities

[John Garry]

+

On 07/03/2022 19:06, Marc Zyngier wrote:
> When booting with maxcpus=<small number>, interrupt controllers
> such as the GICv3 ITS may not be able to satisfy the affinity of
> some managed interrupts, as some of the HW resources are simply
> not available.
>
> In order to deal with this, do not try to activate such interrupt
> if there is no online CPU capable of handling it. Instead, place
> it in shutdown state. Once a capable CPU shows up, it will be
> activated.
>
> Reported-by: John Garry <john.garry@xxxxxxxxxx>
> Reported-by: David Decotigny <ddecotig@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>

Tested-by: John Garry <john.garry@xxxxxxxxxx>

> ---

JFYI, I could not recreate the same crash reported in the original 
thread for "nohz_full=5-127 isolcpus=nohz,domain,managed_irq,5-127 
maxcpus=1". Here's just showing what I set via cmdline:

estuary:/$ dmesg | grep -i hz
[    0.000000] Kernel command line: BOOT_IMAGE=/john/Image rdinit=/init 
console=ttyS0,115200 no_console_suspend nvme.use_threaded_interrupts=0 
iommu.strict=0 acpi=force earlycon=pl011,mmio32,0x602b0000 
nohz_full=5-127 isolcpus=nohz,domain,managed_irq,5-127 maxcpus=1
[    0.000000] NO_HZ: Full dynticks CPUs: 5-127.
[    0.000000] arch_timer: cp15 timer(s) running at 100.00MHz (phys).
[    0.000000] sched_clock: 57 bits at 100MHz, resolution 10ns, wraps 
every 4398046511100ns
[   15.314258] sbsa-gwdt sbsa-gwdt.0: Initialized with 10s timeout @ 
100000000 Hz, action=0

And for the kernel build:
$ more .config | grep NO_HZ
CONFIG_NO_HZ_COMMON=y
# CONFIG_NO_HZ_IDLE is not set
CONFIG_NO_HZ_FULL=y
# CONFIG_NO_HZ is not set
$

Thanks,
John
>   kernel/irq/msi.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
> index 2bdfce5edafd..aa84ce84c2ec 100644
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -818,6 +818,18 @@ static int msi_init_virq(struct irq_domain *domain, int virq, unsigned int vflag
>   		irqd_clr_can_reserve(irqd);
>   		if (vflags & VIRQ_NOMASK_QUIRK)
>   			irqd_set_msi_nomask_quirk(irqd);
> +
> +		/*
> +		 * If the interrupt is managed but no CPU is available
> +		 * to service it, shut it down until better times.
> +		 */
> +		if ((vflags & VIRQ_ACTIVATE) &&
> +		    irqd_affinity_is_managed(irqd) &&
> +		    !cpumask_intersects(irq_data_get_affinity_mask(irqd),
> +					cpu_online_mask)) {
> +			    irqd_set_managed_shutdown(irqd);
> +			    return 0;
> +		    }
>   	}
>   
>   	if (!(vflags & VIRQ_ACTIVATE))