linux-kernel - Re: [PATCH] irqchip/gic: add WARN

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Message-ID: <36538faa77fd0e34f559ec547b983c72@kernel.org>
Date:   Tue, 29 Dec 2020 09:27:40 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Yejune Deng <yejune.deng@...il.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irqchip/gic: add WARN_ON() to facilitate backtracking

Yejune,

On 2020-12-29 07:15, Yejune Deng wrote:
> There is two function gic_of_init() and gic_of_init_child() called
> gic_of_setup(),so add WARN_ON() to facilitate backtracking.
> 
> Signed-off-by: Yejune Deng <yejune.deng@...il.com>
> ---
>  drivers/irqchip/irq-gic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index b1d9c22..7c11705 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -1380,7 +1380,7 @@ static bool gic_check_eoimode(struct device_node
> *node, void __iomem **base)
> 
>  static int gic_of_setup(struct gic_chip_data *gic, struct device_node 
> *node)
>  {
> -	if (!gic || !node)
> +	if (WARN_ON(!gic || !node))
>  		return -EINVAL;
> 
>  	gic->raw_dist_base = of_iomap(node, 0);

I don't immediately see what you gain with this. If you end-up here
with NULL pointers, that either because:

- you have failed to allocate the GIC private data structure:
   but as it turns out, these allocations either cannot fail (gic_data[]
   is static), or the dynamic allocation in gic_of_init_child() is 
already
   checked.

- node is NULL: both paths already check for a NULL node, so that cannot
   fail either.

My conclusion is that these checks can never trigger, and we should be
able to *remove* them altogether.

Am I missing something?

         M.
-- 
Jazz is not dead. It just smells funny...