linux-kernel - Re: [PATCH] x86/apic: Fix suspicious RCU usage in smp_trace_call_function

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Date:   Thu, 15 Sep 2016 10:58:04 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Wanpeng Li <kernellwp@...il.com>
cc:     linux-kernel@...r.kernel.org, Wanpeng Li <wanpeng.li@...mail.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/apic: Fix suspicious RCU usage in
 smp_trace_call_function_interrupt

On Thu, 15 Sep 2016, Wanpeng Li wrote:
> ---
>  arch/x86/include/asm/apic.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 1243577..71c1fe2 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -650,8 +650,8 @@ static inline void entering_ack_irq(void)
>  
>  static inline void ipi_entering_ack_irq(void)
>  {
> -	ack_APIC_irq();
>  	irq_enter();
> +	ack_APIC_irq();
>  }

which makes ipi_entering_ack_irq() the same as entering_ack_irq() and
therefor pointless.

Looking further we have the same issue in exiting_ack_irq() where we call
ack_APIC_irq() after irq_exit().

Thanks,

	tglx