linux-kernel - Re: [PATCHv3 1/3] kernel/irq: make irq_{enter, exit}() in handle_domain

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Date:   Fri, 1 Oct 2021 22:33:22 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Joey Gouly <joey.gouly@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Julien Thierry <julien.thierry@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yuichi Ito <ito-yuichi@...itsu.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/3] kernel/irq: make irq_{enter, exit}() in
 handle_domain_irq() arch optional

On Fri, Oct 01, 2021 at 10:15:16AM +0100, Marc Zyngier wrote:
> On Thu, 30 Sep 2021 14:17:06 +0100,
> Pingfan Liu <kernelfans@...il.com> wrote:
> > 
> > When an IRQ is taken, some accounting needs to be performed to enter and
> > exit IRQ context around the IRQ handler. Historically arch code would
> > leave this to the irqchip or core IRQ code, but these days we want this
> > to happen in exception entry code, and architectures such as arm64 do
> > this.
> > 
> > Currently handle_domain_irq() performs this entry/exit accounting, and
> > if used on an architecture where the entry code also does this, the
> > entry/exit accounting will be performed twice per IRQ. This is
> > problematic as core RCU code such as rcu_is_cpu_rrupt_from_idle()
> > depends on this happening once per IRQ, and will not detect quescent
> > periods correctly, leading to stall warnings.
> > 
> > As irqchip drivers which use handle_domain_irq() need to work on
> > architectures with or without their own entry/exit accounting, this
> > patch makes handle_domain_irq() conditionally perform the entry
> > accounting depending on a new HAVE_ARCH_IRQENTRY Kconfig symbol that
> > architectures can select if they perform this entry accounting
> > themselves.
> > 
> > For architectures which do not select the symbol. there should be no
> > functional change as a result of this patch.
> > 
> > Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> > Reviewed-by: Mark Rutland <mark.rutland@....com>
> > Cc: "Paul E. McKenney" <paulmck@...nel.org>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Marc Zyngier <maz@...nel.org>
> > Cc: Joey Gouly <joey.gouly@....com>
> > Cc: Sami Tolvanen <samitolvanen@...gle.com>
> > Cc: Julien Thierry <julien.thierry@....com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Yuichi Ito <ito-yuichi@...itsu.com>
> > Cc: linux-kernel@...r.kernel.org
> > To: linux-arm-kernel@...ts.infradead.org
> > ---
> >  kernel/irq/Kconfig   | 3 +++
> >  kernel/irq/irqdesc.c | 4 ++++
> >  2 files changed, 7 insertions(+)
> > 
> > diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
> > index fbc54c2a7f23..defa1db2d664 100644
> > --- a/kernel/irq/Kconfig
> > +++ b/kernel/irq/Kconfig
> > @@ -100,6 +100,9 @@ config IRQ_MSI_IOMMU
> >  config HANDLE_DOMAIN_IRQ
> >  	bool
> >  
> > +config HAVE_ARCH_IRQENTRY
> > +	bool
> > +
> >  config IRQ_TIMINGS
> >  	bool
> >  
> > diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> > index 4e3c29bb603c..fd5dd9d278b5 100644
> > --- a/kernel/irq/irqdesc.c
> > +++ b/kernel/irq/irqdesc.c
> > @@ -693,7 +693,9 @@ int handle_domain_irq(struct irq_domain *domain,
> >  	struct irq_desc *desc;
> >  	int ret = 0;
> >  
> > +#ifndef CONFIG_HAVE_ARCH_IRQENTRY
> >  	irq_enter();
> > +#endif
> 
> nit: I tend to prefer the 'if (!IS_ENABLED(CONFIG_*))' approach.
> 
I check the irqdesc.c, the other macro conditional statements have the style
"#ifdef". So if using 'if (!IS_ENABLED(CONFIG_*))', the file looks a
little disharmony.

> >  
> >  	/* The irqdomain code provides boundary checks */
> >  	desc = irq_resolve_mapping(domain, hwirq);
> > @@ -702,7 +704,9 @@ int handle_domain_irq(struct irq_domain *domain,
> >  	else
> >  		ret = -EINVAL;
> >  
> > +#ifndef CONFIG_HAVE_ARCH_IRQENTRY
> >  	irq_exit();
> > +#endif
> >  	set_irq_regs(old_regs);
> >  	return ret;
> >  }
> 
> Apart from that:
> 
> Reviewed-by: Marc Zyngier <maz@...nel.org>
> 
I am not sure whether you agree with my opinion about the style of macro
and hesitate to include your Reviewed-by.

Could you kindly give your Reviewed-by to my V4, if it is OK for you?


Thanks

	Pingfan