Re: [PATCH][2.5] avoid scribbling in IDT with high interrupt count.

[Linus Torvalds]

On Mon, 7 Apr 2003, Zwane Mwaikambo wrote:
>
> On systems with high interrupt counts we end up overshooting the 
> interrupt[] array and dumping garbage entry points into the idt. This 
> patch checks for out of bounds access during ioapic setup as well as 
> returning -ENOSPC when we run out of vectors to assign in 
> assign_irq_vector, thus allowing us to remove the panic and boot a 320 
> interrupt source system with 2.5.66.

Zwane - is there any reason we couldn't just start re-using irq vector
offsets when this happens? We already re-use the vectors themselves, so 
restarting the offset pointer shouldn't really _change_ anything.

In other words, I'm wondering if this simpler patch wouldn't be sufficient 
instead?

Can you please test this, and re-submit (and if you can explain why your 
patch is better, please do so - I have nothing fundamentally against it, I 
just want to understand _why_ the complexity is needed).

Thanks,

		Linus

--- 1.58/arch/i386/kernel/io_apic.c	Thu Mar 20 03:11:41 2003
+++ edited/arch/i386/kernel/io_apic.c	Mon Apr  7 08:25:48 2003
@@ -1110,12 +1110,9 @@
 		goto next;
 
 	if (current_vector > FIRST_SYSTEM_VECTOR) {
-		offset++;
+		offset = (offset+1) & 7;
 		current_vector = FIRST_DEVICE_VECTOR + offset;
 	}
-
-	if (current_vector == FIRST_SYSTEM_VECTOR)
-		panic("ran out of interrupt sources!");
 
 	IO_APIC_VECTOR(irq) = current_vector;
 	return current_vector;