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

From: Armin Steinhoff
Date: Thu Feb 21 2013 - 02:30:53 EST

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 ....


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.



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;
snprintf(mem, IOAPIC_RESOURCE_NAME_SIZE, "IOAPIC %u", i);

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