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

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Date:   Mon, 19 Sep 2016 10:10:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] x86/apic: Fix suspicious RCU usage in
 smp_trace_call_function_interrupt

On Thu, Sep 15, 2016 at 10:58:04AM +0200, Thomas Gleixner wrote:
> 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.

entering_ack_irq() seems to use entering_irq() instead of irq_enter().
Which is close but not the same. This thing seems to also do
exit_idle().

Now, there's only a handfull of ipi_entering_ack_irq() users, and it
doesn't seem to make sense to me to only call exit_idle() on IPIs, why
don't we need to call exit_idle() on regular IRQs ?!

All in all, that stuff is crufty and needs a cleanup I'd say.