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Date:   Thu, 21 May 2020 15:06:16 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Anup Patel <Anup.Patel@....com>
CC:     Paul Walmsley <paul.walmsley@...ive.com>, tglx@...utronix.de,
        jason@...edaemon.net, Marc Zyngier <maz@...nel.org>,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        anup@...infault.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Anup Patel <Anup.Patel@....com>,
        stable@...r.kernel.org
Subject:     Re: [PATCH v2 2/3] irqchip/sifive-plic: Setup cpuhp once after boot CPU handler is present

On Mon, 18 May 2020 02:14:40 PDT (-0700), Anup Patel wrote:
> For multiple PLIC instances, the plic_init() is called once for each
> PLIC instance. Due to this we have two issues:
> 1. cpuhp_setup_state() is called multiple times
> 2. plic_starting_cpu() can crash for boot CPU if cpuhp_setup_state()
>    is called before boot CPU PLIC handler is available.
>
> This patch fixes both above issues.
>
> Fixes: f1ad1133b18f ("irqchip/sifive-plic: Add support for multiple PLICs")
> Cc: stable@...r.kernel.org
> Signed-off-by: Anup Patel <anup.patel@....com>
> ---
>  drivers/irqchip/irq-sifive-plic.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
> index 9f7f8ce88c00..6c54abf5cc5e 100644
> --- a/drivers/irqchip/irq-sifive-plic.c
> +++ b/drivers/irqchip/irq-sifive-plic.c
> @@ -76,6 +76,7 @@ struct plic_handler {
>  	void __iomem		*enable_base;
>  	struct plic_priv	*priv;
>  };
> +static bool plic_cpuhp_setup_done;
>  static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
>
>  static inline void plic_toggle(struct plic_handler *handler,
> @@ -285,6 +286,7 @@ static int __init plic_init(struct device_node *node,
>  	int error = 0, nr_contexts, nr_handlers = 0, i;
>  	u32 nr_irqs;
>  	struct plic_priv *priv;
> +	struct plic_handler *handler;
>
>  	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
>  	if (!priv)
> @@ -313,7 +315,6 @@ static int __init plic_init(struct device_node *node,
>
>  	for (i = 0; i < nr_contexts; i++) {
>  		struct of_phandle_args parent;
> -		struct plic_handler *handler;
>  		irq_hw_number_t hwirq;
>  		int cpu, hartid;
>
> @@ -367,9 +368,18 @@ static int __init plic_init(struct device_node *node,
>  		nr_handlers++;
>  	}
>
> -	cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
> +	/*
> +	 * We can have multiple PLIC instances so setup cpuhp state only
> +	 * when context handler for current/boot CPU is present.
> +	 */
> +	handler = this_cpu_ptr(&plic_handlers);
> +	if (handler->present && !plic_cpuhp_setup_done) {
> +		cpuhp_setup_state(CPUHP_AP_IRQ_SIFIVE_PLIC_STARTING,
>  				  "irqchip/sifive/plic:starting",
>  				  plic_starting_cpu, plic_dying_cpu);
> +		plic_cpuhp_setup_done = true;

So presumably something else is preventing multiple plic_init() calls from
executing at the same time?  Assuming that's the case

Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@...gle.com>

> +	}
> +
>  	pr_info("mapped %d interrupts with %d handlers for %d contexts.\n",
>  		nr_irqs, nr_handlers, nr_contexts);
>  	set_handle_irq(plic_handle_irq);

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