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Subject: Re: [PATCH v2 1/7] entry: add arch_in_rcu_eqs()
From:   Nicolas Saenz Julienne <nsaenzju@redhat.com>
To:     Mark Rutland <mark.rutland@arm.com>, linux-kernel@vger.kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>
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Date:   Fri, 21 Jan 2022 18:34:55 +0100
In-Reply-To: <20220119105854.3160683-2-mark.rutland@arm.com>
References: <20220119105854.3160683-1-mark.rutland@arm.com>
         <20220119105854.3160683-2-mark.rutland@arm.com>
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On Wed, 2022-01-19 at 10:58 +0000, Mark Rutland wrote:
> All architectures have an interruptible RCU extended quiescent state
> (EQS) as part of their idle sequences, where interrupts can occur
> without RCU watching. Entry code must account for this and wake RCU as
> necessary; the common entry code deals with this in irqentry_enter() by
> treating any interrupt from an idle thread as potentially having
> occurred with an EQS and waking RCU for the duration of the interrupt
> via rcu_irq_enter() .. rcu_irq_exit().
> 
> Some architectures may have other interruptible EQSs which require
> similar treatment. For example, on s390 is it necessary to enable
> interrupts around guest entry in the middle of a period where core KVM
> code has entered an EQS.
> 
> So that architectueres can wake RCU in these cases, this patch adds a
> new arch_in_rcu_eqs() hook to the common entry code which is checked in
> addition to the existing is_idle_thread() check, with RCU woken if
> either returns true. A default implementation is provided which always
> returns false, which suffices for most architectures.
> 
> As no architectures currently implement arch_in_rcu_eqs(), there should
> be no functional change as a result of this patch alone. A subsequent
> patch will add an s390 implementation to fix a latent bug with missing
> RCU wakeups.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
> Cc: Heiko Carstens <hca@linux.ibm.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Sven Schnelle <svens@linux.ibm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---

Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>

Thanks,

-- 
Nicolás Sáenz