Messages in this thread | | | Date | Fri, 01 Oct 2021 10:22:50 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCHv3 3/3] arm64/entry-common: supplement irq accounting |
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On Thu, 30 Sep 2021 14:53:14 +0100, Mark Rutland <mark.rutland@arm.com> wrote: > > On Thu, Sep 30, 2021 at 09:17:08PM +0800, Pingfan Liu wrote: > > At present, the irq entry/exit accounting, which is performed by > > handle_domain_irq(), overlaps with arm64 exception entry code somehow. > > > > By supplementing irq accounting on arm64 exception entry code, the > > accounting in handle_domain_irq() can be dropped totally by selecting > > the macro HAVE_ARCH_IRQENTRY. > > I think we need to be more thorough and explain the specific problem and > solution. How about we crib some wording from patch 1, and say: > > arm64: entry: avoid double-accounting IRQ RCU entry > > When an IRQ is taken, some accounting needs to be performed to enter > and exit IRQ context around the IRQ handler. On arm64 some of this > accounting is performed by both the architecture code and the IRQ > domain code, resulting in calling rcu_irq_enter() twice per exception > entry, violating the expectations of the core RCU code, and resulting > in failing to identify quiescent periods correctly (e.g. in > rcu_is_cpu_rrupt_from_idle()). > > To fix this, we must perform all the accounting from the architecture > code. We prevent the IRQ domain code from performing any accounting by > selecting HAVE_ARCH_IRQENTRY, and must call irq_enter_rcu() and > irq_exit_rcu() around invoking the root IRQ handler. > > When we take a pNMI from a context with IRQs disabled, we'll perform > the necessary accounting as part of arm64_enter_nmi() and > arm64_exit_nmi(), and should only call irq_enter_rcu() and > irq_exit_rcu() when we may have taken a regular interrupt. > > That way it's clear what specifically the overlap is and the problem(s) > it results in. The bit at the end explains why we don't call > irq_{enter,exit}_rcu() when we're certain we've taken a pNMI. > > > Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > > Cc: "Paul E. McKenney" <paulmck@kernel.org> > > Cc: Catalin Marinas <catalin.marinas@arm.com> > > Cc: Will Deacon <will@kernel.org> > > Cc: Mark Rutland <mark.rutland@arm.com> > > Cc: Marc Zyngier <maz@kernel.org> > > Cc: Joey Gouly <joey.gouly@arm.com> > > Cc: Sami Tolvanen <samitolvanen@google.com> > > Cc: Julien Thierry <julien.thierry@arm.com> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: Yuichi Ito <ito-yuichi@fujitsu.com> > > Cc: linux-kernel@vger.kernel.org > > To: linux-arm-kernel@lists.infradead.org > > --- > > arch/arm64/Kconfig | 1 + > > arch/arm64/kernel/entry-common.c | 4 ++++ > > 2 files changed, 5 insertions(+) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 5c7ae4c3954b..d29bae38a951 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -98,6 +98,7 @@ config ARM64 > > select ARCH_HAS_UBSAN_SANITIZE_ALL > > select ARM_AMBA > > select ARM_ARCH_TIMER > > + select HAVE_ARCH_IRQENTRY > > Please put this with the other HAVE_ARCH_* entries in > arch/arm64/Kconfig -- it should be between HAVE_ARCH_HUGE_VMAP and > HAVE_ARCH_JUMP_LABEL to keep that in alphabetical order. > > With that and the title and commit message above: > > Reviewed-by: Mark Rutland <mark.rutland@arm.com>
With the above changes,
Reviewed-by: Marc Zyngier <maz@kernel.org>
M.
-- Without deviation from the norm, progress is not possible.
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