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

[Guo Zhengkui]

On 2022/3/10 16:27, Marc Zyngier wrote:
> On Thu, 10 Mar 2022 05:02:38 +0000,
> Guo Zhengkui <guozhengkui@xxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx/
> > https://lore.kernel.org/all/YbBGGI9wQenI4kP7@xxxxxxxxx/
> > https://lore.kernel.org/all/20211209062441.9856-1-guozhengkui@xxxxxxxx/
> >
> > Signed-off-by: Guo Zhengkui <guozhengkui@xxxxxxxx>
> > ---
> >   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;
>