linux-kernel - Re: [PATCH] irqchip/gic-v3-its: fix ITS queue timeout

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Message-ID: <834fde1b-5ae0-afc6-283f-2a470757e54a@arm.com>
Date:   Tue, 5 Jun 2018 11:16:05 +0100
From:   Julien Thierry <julien.thierry@....com>
To:     Yang Yingliang <yangyingliang@...wei.com>, marc.zyngier@....com
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] irqchip/gic-v3-its: fix ITS queue timeout

Hi Yang,

On 05/06/18 07:30, Yang Yingliang wrote:
> When the kernel booted with maxcpus=x, 'x' is smaller
> than actual cpu numbers, the TAs of offline cpus won't
> be set to its->collection.
> 
> If LPI is bind to offline cpu, sync cmd will use zero TA,
> it leads to ITS queue timeout.  Fix this by choosing a
> online cpu, if there is no online cpu in cpu_mask.
> 
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
>   drivers/irqchip/irq-gic-v3-its.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 5416f2b..edd92a9 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -2309,7 +2309,9 @@ static int its_irq_domain_activate(struct irq_domain *domain,
>   		cpu_mask = cpumask_of_node(its_dev->its->numa_node);
>   
>   	/* Bind the LPI to the first possible CPU */
> -	cpu = cpumask_first(cpu_mask);
> +	cpu = cpumask_first_and(cpu_mask, cpu_online_mask);
> +	if (!cpu_online(cpu))

Testing for cpu being online here feels a bit redundant.

Since cpu is online if the cpumask_first_and returns a valid cpu, I 
think you could replace this test with:

	if (cpu >= nr_cpu_ids)

> +		cpu = cpumask_first(cpu_online_mask);
>   	its_dev->event_map.col_map[event] = cpu;
>   	irq_data_update_effective_affinity(d, cpumask_of(cpu));
>   
> @@ -2466,7 +2468,10 @@ static int its_vpe_set_affinity(struct irq_data *d,
>   				bool force)
>   {
>   	struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
> -	int cpu = cpumask_first(mask_val);
> +	int cpu = cpumask_first_and(mask_val, cpu_online_mask);
> +
> +	if (!cpu_online(cpu))

Same thing here.

> +		cpu = cpumask_first(cpu_online_mask);
>   
>   	/*
>   	 * Changing affinity is mega expensive, so let's be as lazy as
> 

Cheers,

-- 
Julien Thierry