From: Chris Lalancette <clalance@redhat.com>
Date: Wed, 21 Nov 2007 10:23:09 -0500
Subject: [xen] avoid dom0 hang when disabling pirq's
Message-id: 47444D5D.2030806@redhat.com
O-Subject: [RHEL5.2 PATCH]: Avoid Xen dom0 hang when disabling pirq's
Bugzilla: 372741

All,
     Attached is a patch to fix BZ 372741.  The Lenovo *61 laptops have some
sort of firmware bug where they continually send interrupts to a line that no
driver is ACK'ing.  After 999,990 of 100,000 interrupts are ignored, the kernel
decides to disable that interrupt line.  In the bare-metal kernel, this is done
by masking out the interrupt line on the IOAPIC.  However, the Xen kernel
currently just masks out the event channel, meaning that the physical hardware
is still firing interrupts, but they never get delivered anywhere, which causes
a deadlock and all interrupts to cease on the machine.

The attached patch fixes the hang by doing a hypercall when disabling the IRQ;
in turn, this makes the HV actually mask out that line on the IOAPIC, which is
the right thing to do.

Successfully tested by me on the Lenovo T61 laptop; before the patch, the
machine would hang after 100,000 interrupts; after the patch, the machine
properly disables that interrupt line.  Note that there is still a bug somewhere
in the laptop, either with the firmware or with the interrupt routing, but that
is not a Xen-specific problem.

This has been committed in upstream Xen:
http://xenbits.xensource.com/staging/linux-2.6.18-xen.hg?rev/51b2b0d0921c

Please review and ACK.

Chris Lalancette

Acked-by: Alan Cox <alan@redhat.com>
Acked-by: Jarod Wilson <jwilson@redhat.com>

Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Don Dutile <ddutile@redhat.com>

diff --git a/drivers/xen/core/evtchn.c b/drivers/xen/core/evtchn.c
index 77ca1bf..75ad2e5 100644
--- a/drivers/xen/core/evtchn.c
+++ b/drivers/xen/core/evtchn.c
@@ -629,20 +629,11 @@ static void shutdown_pirq(unsigned int irq)
 
 static void enable_pirq(unsigned int irq)
 {
-	int evtchn = evtchn_from_irq(irq);
-
-	if (VALID_EVTCHN(evtchn)) {
-		unmask_evtchn(evtchn);
-		pirq_unmask_notify(irq_to_pirq(irq));
-	}
+	startup_pirq(irq);
 }
 
 static void disable_pirq(unsigned int irq)
 {
-	int evtchn = evtchn_from_irq(irq);
-
-	if (VALID_EVTCHN(evtchn))
-		mask_evtchn(evtchn);
 }
 
 static void ack_pirq(unsigned int irq)
@@ -661,7 +652,10 @@ static void end_pirq(unsigned int irq)
 {
 	int evtchn = evtchn_from_irq(irq);
 
-	if (VALID_EVTCHN(evtchn) && !(irq_desc[irq].status & IRQ_DISABLED)) {
+	if ((irq_desc[irq].status & (IRQ_DISABLED|IRQ_PENDING)) ==
+	    (IRQ_DISABLED|IRQ_PENDING)) {
+		shutdown_pirq(irq);
+	} else if (VALID_EVTCHN(evtchn)) {
 		unmask_evtchn(evtchn);
 		pirq_unmask_notify(irq_to_pirq(irq));
 	}