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Date: Thu, 10 Mar 2022 08:27:24 +0000 From: Marc Zyngier <maz@...nel.org> To: Guo Zhengkui <guozhengkui@...o.com> Cc: Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>, Alyssa Rosenzweig <alyssa@...enzweig.io>, Thomas Gleixner <tglx@...utronix.de>, linux-arm-kernel@...ts.infradead.org (moderated list:ARM/APPLE MACHINE SUPPORT), linux-kernel@...r.kernel.org (open list:IRQCHIP DRIVERS), zhengkui_guo@...look.com Subject: Re: [PATCH] irqchip/apple-aic: application of sizeof() to a pointer 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. 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. 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; -- Without deviation from the norm, progress is not possible.
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