linux-kernel - Re: [PATCHv4 0/3] arm64/irqentry: remove duplicate housekeeping of rcu

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Message-ID: <87v92crbtf.wl-maz@kernel.org>
Date:   Mon, 04 Oct 2021 17:31:40 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        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: [PATCHv4 0/3] arm64/irqentry: remove duplicate housekeeping of rcu

On Fri, 01 Oct 2021 15:44:03 +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.
> 
> V3 -> V4:
>   address Signed-off-by in [2/3]
>   improve commit log in [3/3]
> 
> V2 -> V3:
>   Drop other patches and concentrate on the purpose of [3-4/5] of V2.
>   And lift the level, where to add {irq_enter,exit}_rcu(), from the
>   interrupt controler to exception entry  
> 
> History:
> V1: https://lore.kernel.org/linux-arm-kernel/1607912752-12481-1-git-send-email-kernelfans@gmail.com
> V2: https://lore.kernel.org/linux-arm-kernel/20210924132837.45994-1-kernelfans@gmail.com
> V3: https://lore.kernel.org/linux-arm-kernel/20210930131708.35328-1-kernelfans@gmail.com
> 
> 
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> 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
> 
> Mark Rutland (1):
>   arm64: entry: refactor EL1 interrupt entry logic
> 
> Pingfan Liu (2):
>   kernel/irq: make irq_{enter,exit}() in handle_domain_irq() arch
>     optional
>   arm64: entry: avoid double-accounting IRQ RCU entry
> 
>  arch/arm64/Kconfig               |  1 +
>  arch/arm64/kernel/entry-common.c | 47 +++++++++++++++++---------------
>  kernel/irq/Kconfig               |  3 ++
>  kernel/irq/irqdesc.c             |  4 +++
>  4 files changed, 33 insertions(+), 22 deletions(-)

Given that most of the changes are in the arm64 tree, it'd be good if
the whole series went via the arm64 tree, most probably as a fix.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.