linux-kernel - Re: io_apic.c --> "nr_ioapics" not initialized !

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Message-ID: <5125CD12.2080002@steinhoff.de>
Date:	Thu, 21 Feb 2013 08:30:26 +0100
From:	Armin Steinhoff <armin@...inhoff.de>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>, x86@...nel.org
Subject: Re: io_apic.c --> "nr_ioapics" not initialized !

Thomas Gleixner wrote:
> On Wed, 20 Feb 2013, Armin Steinhoff wrote:
>> after a walk through the module "io_apic.c" in
>> "/usr/src/linux/arch/x86/kernel/apic" I got the impression that the variable
>> "nr_ioapics" is used but isn't initialized !
>> Could it be the source of boot problems ?
> Well no, unless your compiler is silly.
>   
> arch/x86/kernel/apic/io_apic.c:int nr_ioapics;
>
> That's initialized to 0

  My "silly compiler" does it only during load time ....

--Armin

>
>> Dangerous coding stile in "static struct resource * __init
>> ioapic_setup_resources(int nr_ioapics)" ....
> Though the brilliant brain who decided to name the argument of
> ioapic_setup_resources() the same as a global variable and of course
> the call site of it to do:
>
>      ioapic_res = ioapic_setup_resources(nr_ioapics);
>
> Brilliant. Unfortunately that's completely correct C code. Though it's
> confusing as hell and definitely worth to be fixed. Patch below.
>
> Thanks,
>
> 	tglx
>
> Index: linux-2.6/arch/x86/kernel/apic/io_apic.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c
> +++ linux-2.6/arch/x86/kernel/apic/io_apic.c
> @@ -3637,25 +3637,25 @@ void __init setup_ioapic_dest(void)
>   
>   static struct resource *ioapic_resources;
>   
> -static struct resource * __init ioapic_setup_resources(int nr_ioapics)
> +static struct resource * __init ioapic_setup_resources(int cnt)
>   {
>   	unsigned long n;
>   	struct resource *res;
>   	char *mem;
>   	int i;
>   
> -	if (nr_ioapics <= 0)
> +	if (cnt <= 0)
>   		return NULL;
>   
>   	n = IOAPIC_RESOURCE_NAME_SIZE + sizeof(struct resource);
> -	n *= nr_ioapics;
> +	n *= cnt;
>   
>   	mem = alloc_bootmem(n);
>   	res = (void *)mem;
>   
> -	mem += sizeof(struct resource) * nr_ioapics;
> +	mem += sizeof(struct resource) * cnt;
>   
> -	for (i = 0; i < nr_ioapics; i++) {
> +	for (i = 0; i < cnt; i++) {
>   		res[i].name = mem;
>   		res[i].flags = IORESOURCE_MEM | IORESOURCE_BUSY;
>   		snprintf(mem, IOAPIC_RESOURCE_NAME_SIZE, "IOAPIC %u", i);
>

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