Re: [PATCH] x86/irq: Plug vector setup race

[Thomas Gleixner]

On Thu, Jul 24 2025 at 12:49, Thomas Gleixner wrote:

Hogan!

> Hogan reported a vector setup race, which overwrites the interrupt
> descriptor in the per CPU vector array resulting in a disfunctional device.
>
> CPU0				CPU1
> 				interrupt is raised in APIC IRR
> 				but not handled
>   free_irq()
>     per_cpu(vector_irq, CPU1)[vector] = VECTOR_SHUTDOWN;
>
>   request_irq()			common_interrupt()
>   				  d = this_cpu_read(vector_irq[vector]);
>
>     per_cpu(vector_irq, CPU1)[vector] = desc;
>
>     				  if (d == VECTOR_SHUTDOWN)
> 				    this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
>
> free_irq() cannot observe the pending vector in the CPU1 APIC as there is
> no way to query the remote CPUs APIC IRR.
>
> This requires that request_irq() uses the same vector/CPU as the one which
> was freed, but this also can be triggered by a spurious interrupt.
>
> Prevent this by reevaluating vector_irq under the vector lock, which is
> held by the interrupt activation code when vector_irq is updated.

Does this fix your problem?

Thanks,

        tglx