Red Hat 7.1 Linux Beta - beta3
Feb 8, 2001
HW: any / Tested with DL380
2.4.x SMP kernel breaks legacy PIC interrupts 13/2
The following email describes this issue, we also have a preliminary patch
(a one liner) to fix this:
Sent: Wednesday, February 07, 2001 1:53 PM
Subject: [BUG] 2.4.x SMP kernel breaks legacy PIC interrupts 13/2
Compaq leverages IRQ 13, usually used to raise a floating point exception
on Intel pre-Pentium systems, to trigger management interrupts (i.e. on
fan failure, etc.). This interrupt level is usually NOT shareable, but
through some magic, we managed to register an ISR for our management
driver on IRQ 13. In the kernel 2.2.x, this worked fine for both SMP and
UP kernels. On the 2.4.x SMP kernels, we do NOT get any interrupts when
using request_irq() for IRQ 13.
If you boot the SMP kernel with the 'noapic' parameter, the interrupt
We are aware that IRQ 2 and IRQ 13 will be always routed through the
legacy 8259A PIC as opposed to the IO-APIC. If we change the kernel to
route IRQ 13 through the APIC, everything works fine. Furthermore, if we
route any other working interrupt through the PIC, it does not work. It
appears to be related to putting the PIC into auto-EOI mode. The 2.4 SMP
kernel puts the PIC in auto-EOI mode while setting up the timer
interrupt. See init_8259A(1) in the check_timer routine in
PIC and APIC routed interrupts do not coexist peacefully in the 2.4.x SMP
kernel. We need to figure out why PIC interrupts don't work with the APIC
interrupts enabled, or stop forcing IRQ 2 and 13 to the PIC when APIC
interrupts are enabled. As it is right now, you will never see an IRQ 2
or 13 while in APIC mode on the 2.4.x SMP kernel, which makes the code
carefully preserving PIC interrupts superfluous. If fixing this kernel
flaw turns out to be too involved, at the very least, we would like to
suggest the code forcing IRQ's 2 and 13 onto the PIC be removed from the
Compaq Bug #: 193820
Compaq considers this defect a MUST-FIX for Florence.
This defect is considered MUST-FIX for Florence Gold release
I don't see the patch. Could you post it again ?
Created attachment 9539 [details]
APIC IRQ13 patch
merged; will be in next kernel build
I will close this bug as deferred as your patch will be in the next build.
Oops, "next build" should be RAWHIDE resolution.