Message-ID: <2025082243-urging-outdoors-aa35@gregkh>
Date: Fri, 22 Aug 2025 10:57:56 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, hpa@...or.com, prarit@...hat.com,
	x86@...nel.org, stable@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6.6 RESEND 2/2] x86/irq: Plug vector setup race

On Fri, Aug 22, 2025 at 03:38:25AM +0000, Jinjie Ruan wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> commit ce0b5eedcb753697d43f61dd2e27d68eb5d3150f upstream.
> 
> 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@...r.kernel.org#6.6.x
> Cc: gregkh@...uxfoundation.org
> Reported-by: Hogan Wang <hogan.wang@...wei.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Hogan Wang <hogan.wang@...wei.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.
>   Conflicts 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@...wei.com>
> ---
>  arch/x86/kernel/irq.c | 65 +++++++++++++++++++++++++++++++++----------
>  1 file changed, 51 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index 1f066268ec29..29d0fc94232e 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -242,24 +242,59 @@ static __always_inline void handle_irq(struct irq_desc *desc,
>  		__handle_irq(desc, regs);
>  }
>  
> -static __always_inline void call_irq_handler(int vector, struct pt_regs *regs)
> +static struct irq_desc *reevaluate_vector(int vector)
>  {
> -	struct irq_desc *desc;
> +	struct irq_desc *desc = __this_cpu_read(vector_irq[vector]);
> +
> +	if (!IS_ERR_OR_NULL(desc))
> +		return desc;
> +
> +	if (desc == VECTOR_UNUSED)
> +		pr_emerg_ratelimited("No irq handler for %d.%u\n", smp_processor_id(), vector);
> +	else
> +		__this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
> +	return NULL;
> +}
> +
> +static __always_inline bool call_irq_handler(int vector, struct pt_regs *regs)
> +{
> +	struct irq_desc *desc = __this_cpu_read(vector_irq[vector]);
>  
> -	desc = __this_cpu_read(vector_irq[vector]);
>  	if (likely(!IS_ERR_OR_NULL(desc))) {
>  		handle_irq(desc, regs);
> -	} else {
> -		apic_eoi();
> -
> -		if (desc == VECTOR_UNUSED) {
> -			pr_emerg_ratelimited("%s: %d.%u No irq handler for vector\n",
> -					     __func__, smp_processor_id(),
> -					     vector);
> -		} else {
> -			__this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
> -		}
> +		return true;
>  	}
> +
> +	/*
> +	 * Reevaluate with vector_lock held to prevent a race against
> +	 * request_irq() setting up the vector:
> +	 *
> +	 * 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);
> +	 *
> +	 * This requires that the same vector on the same target CPU is
> +	 * handed out or that a spurious interrupt hits that CPU/vector.
> +	 */
> +	lock_vector_lock();
> +	desc = reevaluate_vector(vector);
> +	unlock_vector_lock();
> +
> +	if (!desc)
> +		return false;
> +
> +	handle_irq(desc, regs);
> +	return true;
>  }
>  
>  /*
> @@ -273,7 +308,9 @@ DEFINE_IDTENTRY_IRQ(common_interrupt)
>  	/* entry code tells RCU that we're not quiescent.  Check it. */
>  	RCU_LOCKDEP_WARN(!rcu_is_watching(), "IRQ failed to wake up RCU");
>  
> -	call_irq_handler(vector, regs);
> +	if (unlikely(!call_irq_handler(vector, regs)))
> +		apic_eoi();
> +

This chunk does not look correct.  The original commit did not have
this, so why add it here?  Where did it come from?

The original patch said:
	-       if (unlikely(call_irq_handler(vector, regs)))
	+       if (unlikely(!call_irq_handler(vector, regs)))

And was not an if statement.

So did you forget to backport something else here?  Why is this not
identical to what the original was?

thanks,

greg k-h

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