Re: [PATCH v6.6 2/2] x86/irq: Plug vector setup race

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Aug 21, 2025 at 01:12:28PM +0000, Jinjie Ruan wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> 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.
> 
> Interestingly enough this problem managed to be hidden for more than a
> decade.
> 
> Prevent this by reevaluating vector_irq under the vector lock, which is
> held by the interrupt activation code when vector_irq is updated.
> 
> To avoid ifdeffery or IS_ENABLED() nonsense, move the
> [un]lock_vector_lock() declarations out under the
> CONFIG_IRQ_DOMAIN_HIERARCHY guard as it's only provided when
> CONFIG_X86_LOCAL_APIC=y.
> 
> The current CONFIG_IRQ_DOMAIN_HIERARCHY guard is selected by
> CONFIG_X86_LOCAL_APIC, but can also be selected by other parts of the
> Kconfig system, which makes 32-bit UP builds with CONFIG_X86_LOCAL_APIC=n
> fail.
> 
> Can we just get rid of this !APIC nonsense once and forever?
> 
> Fixes: 9345005f4eed ("x86/irq: Fix do_IRQ() interrupt warning for cpu hotplug retriggered irqs")
> Cc: stable@vger.kernel.org#6.6.x
> Cc: gregkh@linuxfoundation.org
> Reported-by: Hogan Wang <hogan.wang@huawei.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: Hogan Wang <hogan.wang@huawei.com>
> Link: https://lore.kernel.org/all/draft-87ikjhrhhh.ffs@tglx
> [ Conflicts in arch/x86/kernel/irq.c because call_irq_handler() has been
>   refactored to do apic_eoi() according to the return value.
>   Conflincts in arch/x86/include/asm/hw_irq.h because (un)lock_vector_lock()
>   are already controlled by CONFIG_X86_LOCAL_APIC. ]
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---
>  arch/x86/kernel/irq.c | 65 +++++++++++++++++++++++++++++++++----------
>  1 file changed, 51 insertions(+), 14 deletions(-)
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>