linux-kernel - Re: [patch 3/8] x86/apic: Provide apic_ack

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Date:   Tue, 5 Jun 2018 19:31:11 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Song Liu <liu.song.a23@...il.com>,
        Joerg Roedel <jroedel@...e.de>,
        Mike Travis <mike.travis@....com>, <stable@...r.kernel.org>
Subject: Re: [patch 3/8] x86/apic: Provide apic_ack_irq()

Hi Thomas,

At 06/04/2018 11:33 PM, Thomas Gleixner wrote:
> apic_ack_edge() is explicitely for handling interrupt affinity cleanup when
> interrupt remapping is not available or disable.
> 
> Remapped interrupts and also some of the platform specific special
> interrupts, e.g. UV, invoke ack_APIC_irq() directly.
> 
> To address the issue of failing an affinity update with -EBUSY the delayed
> affinity mechanism can be reused, but ack_APIC_irq() does not handle
> that. Adding this to ack_APIC_irq() is not possible, because that function
> is also used for exceptions and directly handled interrupts like IPIs.
> 
> Create a new function, which just contains the conditional invocation of
> irq_move_irq() and the final ack_APIC_irq(). Making the invocation of
> irq_move_irq() conditional avoids the out of line call if the pending bit
> is not set.
> 
> Reuse the new function in apic_ack_edge().
> 
> Preparatory change for the real fix
> 
> Fixes: dccfe3147b42 ("x86/vector: Simplify vector move cleanup")
> Signed-off-by: Thomas Gleixner<tglx@...utronix.de>
> Cc:stable@...r.kernel.org
> ---
>   arch/x86/include/asm/apic.h   |    2 ++
>   arch/x86/kernel/apic/vector.c |   10 ++++++++--
>   2 files changed, 10 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -436,6 +436,8 @@ static inline void apic_set_eoi_write(vo
>   
>   #endif /* CONFIG_X86_LOCAL_APIC */
>   
> +extern void apic_ack_irq(struct irq_data *data);
> +
>   static inline void ack_APIC_irq(void)
>   {
>   	/*
> --- a/arch/x86/kernel/apic/vector.c
> +++ b/arch/x86/kernel/apic/vector.c
> @@ -809,11 +809,17 @@ static int apic_retrigger_irq(struct irq
>   	return 1;
>   }
>   
> +void apic_ack_irq(struct irq_data *irqd)
> +{
> +	if (unlikely(irqd_is_setaffinity_pending(irqd)))

Affinity pending is also judged in

> +		irq_move_irq(irqd);

If we can remove the if(...) statement here

Thanks,
	dou

> +	ack_APIC_irq();
> +}
> +
>   void apic_ack_edge(struct irq_data *irqd)
>   {
>   	irq_complete_move(irqd_cfg(irqd));
> -	irq_move_irq(irqd);
> -	ack_APIC_irq();
> +	apic_ack_irq(irqd);
>   }
>   
>   static struct irq_chip lapic_controller = {