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

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Date:	Wed, 20 Feb 2013 23:55:01 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Armin Steinhoff <armin@...inhoff.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 !

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

> 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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