linux-kernel - Re: [PATCH] irqchip/apple-aic: application of sizeof() to a pointer

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Date:   Thu, 10 Mar 2022 16:48:07 +0800
From:   Guo Zhengkui <guozhengkui@...o.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Thomas Gleixner <tglx@...utronix.de>,
        "moderated list:ARM/APPLE MACHINE SUPPORT" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:IRQCHIP DRIVERS" <linux-kernel@...r.kernel.org>,
        "zhengkui_guo@...look.com" <zhengkui_guo@...look.com>
Subject: Re: [PATCH] irqchip/apple-aic: application of sizeof() to a pointer

On 2022/3/10 16:27, Marc Zyngier wrote:
> On Thu, 10 Mar 2022 05:02:38 +0000,
> Guo Zhengkui <guozhengkui@...o.com> wrote:
>>
>> `ic->fiq_aff[fiq]` is a pointer to the unnamed struct.
>> `sizeof(ic->fiq_aff[fiq])` intends to get the size of this pointer. But
>> readers may get confused. `sizeof(unsigned long)` makes more sense because
>> `unsigned long` has the same size of pointer.
> 
> More sense? It really depends on who reads the code.
> 
>>
>> reference:
>> https://lore.kernel.org/all/Ya%2FeUbdN1+ABFVWf@rowland.harvard.edu/
>> https://lore.kernel.org/all/YbBGGI9wQenI4kP7@kroah.com/
>> https://lore.kernel.org/all/20211209062441.9856-1-guozhengkui@vivo.com/
>>
>> Signed-off-by: Guo Zhengkui <guozhengkui@...o.com>
>> ---
>>   drivers/irqchip/irq-apple-aic.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-apple-aic.c b/drivers/irqchip/irq-apple-aic.c
>> index b40199c6625e..23098b469b1a 100644
>> --- a/drivers/irqchip/irq-apple-aic.c
>> +++ b/drivers/irqchip/irq-apple-aic.c
>> @@ -810,7 +810,7 @@ static void build_fiq_affinity(struct aic_irq_chip *ic, struct device_node *aff)
>>   	if (WARN_ON(n < 0))
>>   		return;
>>   
>> -	ic->fiq_aff[fiq] = kzalloc(sizeof(ic->fiq_aff[fiq]), GFP_KERNEL);
>> +	ic->fiq_aff[fiq] = kzalloc(sizeof(unsigned long), GFP_KERNEL);
> 
> And by doing that, you are making even more difficult to spot the
> glaring bug that is in front of your eyes: we're not trying to
> allocate a pointer, but to allocate the full data structure.
> 

Oh, I surely made a big mistake...

> Nothing went wrong as a 64bit allocation is plenty when you need at
> most 10 bits, but jeez, what a howler. I'm stashing the fixlet below
> on top.
> 

So, will you send this new patch by yourself?

Zhengkui

> Thanks,
> 
> 	M.
> 
> diff --git a/drivers/irqchip/irq-apple-aic.c b/drivers/irqchip/irq-apple-aic.c
> index b40199c6625e..3f1d2f3ccb7f 100644
> --- a/drivers/irqchip/irq-apple-aic.c
> +++ b/drivers/irqchip/irq-apple-aic.c
> @@ -810,7 +810,7 @@ static void build_fiq_affinity(struct aic_irq_chip *ic, struct device_node *aff)
>   	if (WARN_ON(n < 0))
>   		return;
>   
> -	ic->fiq_aff[fiq] = kzalloc(sizeof(ic->fiq_aff[fiq]), GFP_KERNEL);
> +	ic->fiq_aff[fiq] = kzalloc(sizeof(*ic->fiq_aff[fiq]), GFP_KERNEL);
>   	if (!ic->fiq_aff[fiq])
>   		return;
>   
>