linux-kernel - Re: [PATCH v2 2/3] irqdomain: Fix irq_domain_trim

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Date:   Fri, 20 Aug 2021 16:54:21 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Maulik Shah <mkshah@...eaurora.org>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-gpio@...r.kernel.org,
        bjorn.andersson@...aro.org, linus.walleij@...aro.org,
        tkjos@...gle.com, lsrao@...eaurora.org
Subject: Re: [PATCH v2 2/3] irqdomain: Fix irq_domain_trim_hierarchy()

On Thu, 19 Aug 2021 12:53:12 +0100,
Maulik Shah <mkshah@...eaurora.org> wrote:
> 
> Currently tail marker is moving along with parent domain
> irq data. Fix this to initialize only once from where all
> parent domain needs trimming.
> 
> Also correct the valid irq chip check.
> 
> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
> ---
>  kernel/irq/irqdomain.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index 19e83e9..9f6187b 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -1235,7 +1235,7 @@ static int irq_domain_trim_hierarchy(unsigned int virq)
>  	 */
>  	for (irqd = irq_data->parent_data; irqd; irq_data = irqd, irqd = irqd->parent_data) {
>  		/* Can't have a valid irqchip after a trim marker */
> -		if (irqd->chip && tail)
> +		if (!IS_ERR(irqd->chip) && tail)
>  			return -EINVAL;
>  
>  		/* Can't have an empty irqchip before a trim marker */
> @@ -1247,7 +1247,8 @@ static int irq_domain_trim_hierarchy(unsigned int virq)
>  			if (PTR_ERR(irqd->chip) != -ENOTCONN)
>  				return -EINVAL;
>  
> -			tail = irq_data;
> +			if (!tail)
> +				tail = irq_data;
>  		}
>  	}

I think you have the wrong end of the stick. 'tail' represent the
*unique* point in the hierarchy where you can have a trim marker:

(1) If there is a valid irqchip after a trim marker, this is wrong
(2) If there is a trim marker after another trim marker, this is wrong
(3) If there is a NULL irqchip before a trim marker, this is wrong
(4) If there is an error that isn't a trim marker, this is wrong

(1) and (2) are captured by:
		if (irqd->chip && tail)
(3) is captured by:
		if (!irqd->chip && !tail)
(4) is captured by:
		if (IS_ERR(irqd->chip)) {
			/* Only -ENOTCONN is a valid trim marker */
			if (PTR_ERR(irqd->chip) != -ENOTCONN)

The expected usage is that:

- there is a single potential trim marker in the hierarchy
- all the irqd->chip pointers below the marker are NULL
- all the irqd->chip before the marker are neither NULL nor an error

I don't see any bug here.

Thanks,

	M.

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