From mboxrd@z Thu Jan  1 00:00:00 1970
References: <20211108060011.612786-1-florian.bezdeka@siemens.com>
From: Philippe Gerum <rpm@xenomai.org>
Subject: Re: [dovetail][PATCH] x86: pipeline: Fix vector stall after vector
 error handling
Date: Mon, 08 Nov 2021 08:56:24 +0100
In-reply-to: <20211108060011.612786-1-florian.bezdeka@siemens.com>
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To: Florian Bezdeka <florian.bezdeka@siemens.com>
Cc: xenomai@xenomai.org, jan.kiszka@siemens.com, henning.schild@siemens.com


Florian Bezdeka <florian.bezdeka@siemens.com> writes:

> Whenever an IRQ was handled for a vector being NULL or in one of the
> error states the interrupt was not acknowledged at the APIC. That can
> happen if a vector is cleaned up by one of the device drivers while
> there is still one IRQ in flight.
>
> This has two effects:
>   - If the affected vector is re-assigned later, it does not work, the
>     IRQ never makes its way to the CPU
>   - Interrupts with lower priority are no longer delivered to the CPU
>
> The problem was observed on a quite big Intel XEON machine where some
> vectors / irqs were temporary used and cleaned up and re-assigned
> later.
>
> Signed-off-by: Florian Bezdeka <florian.bezdeka@siemens.com>
> ---
>  arch/x86/kernel/irq_pipeline.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kernel/irq_pipeline.c b/arch/x86/kernel/irq_pipeline.c
> index 48d9959bc11a..63de68141b21 100644
> --- a/arch/x86/kernel/irq_pipeline.c
> +++ b/arch/x86/kernel/irq_pipeline.c
> @@ -239,6 +239,8 @@ void arch_handle_irq(struct pt_regs *regs, u8 vector, bool irq_movable)
>  	} else {
>  		desc = __this_cpu_read(vector_irq[vector]);
>  		if (unlikely(IS_ERR_OR_NULL(desc))) {
> +			__ack_APIC_irq();
> +
>  			if (desc == VECTOR_UNUSED) {
>  				pr_emerg_ratelimited("%s: %d.%u No irq handler for vector\n",
>  						__func__, smp_processor_id(),

Ouch. Thanks for digging this. Merged upstream.

-- 
Philippe.