xen/events: don't bind non-percpu VIRQs with percpu chip

commit 77bb3dfd upstream.

A non-percpu VIRQ (e.g., VIRQ_CONSOLE) may be freed on a different
VCPU than it is bound to.  This can result in a race between
handle_percpu_irq() and removing the action in __free_irq() because
handle_percpu_irq() does not take desc->lock.  The interrupt handler
sees a NULL action and oopses.

Only use the percpu chip/handler for per-CPU VIRQs (like VIRQ_TIMER).

  # cat /proc/interrupts | grep virq
   40:      87246          0  xen-percpu-virq      timer0
   44:          0          0  xen-percpu-virq      debug0
   47:          0      20995  xen-percpu-virq      timer1
   51:          0          0  xen-percpu-virq      debug1
   69:          0          0   xen-dyn-virq      xen-pcpu
   74:          0          0   xen-dyn-virq      mce
   75:         29          0   xen-dyn-virq      hvc_console
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
[bwh: Backported to 3.2: adjust filename, context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/tty/hvc/hvc_xen.c

@@ -167,7 +167,7 @@ static int __init xen_hvc_init(void)
 
 	if (xen_initial_domain()) {
 		ops = &dom0_hvc_ops;
-		xencons_irq = bind_virq_to_irq(VIRQ_CONSOLE, 0);
+		xencons_irq = bind_virq_to_irq(VIRQ_CONSOLE, 0, false);
 	} else {
 		if (!xen_start_info->console.domU.evtchn)
 			return -ENODEV;

drivers/xen/events.c

@@ -895,7 +895,7 @@ static int find_virq(unsigned int virq, unsigned int cpu)
 	return rc;
 }
 
-int bind_virq_to_irq(unsigned int virq, unsigned int cpu)
+int bind_virq_to_irq(unsigned int virq, unsigned int cpu, bool percpu)
 {
 	struct evtchn_bind_virq bind_virq;
 	int evtchn, irq, ret;
@@ -909,8 +909,12 @@ int bind_virq_to_irq(unsigned int virq, unsigned int cpu)
 		if (irq == -1)
 			goto out;
 
+		if (percpu)
 			irq_set_chip_and_handler_name(irq, &xen_percpu_chip,
 						      handle_percpu_irq, "virq");
+		else
+			irq_set_chip_and_handler_name(irq, &xen_dynamic_chip,
+						      handle_edge_irq, "virq");
 
 		bind_virq.virq = virq;
 		bind_virq.vcpu = cpu;
@@ -1023,7 +1027,7 @@ int bind_virq_to_irqhandler(unsigned int virq, unsigned int cpu,
 {
 	int irq, retval;
 
-	irq = bind_virq_to_irq(virq, cpu);
+	irq = bind_virq_to_irq(virq, cpu, irqflags & IRQF_PERCPU);
 	if (irq < 0)
 		return irq;
 	retval = request_irq(irq, handler, irqflags, devname, dev_id);

include/xen/events.h

@@ -12,7 +12,7 @@ int bind_evtchn_to_irqhandler(unsigned int evtchn,
 			      irq_handler_t handler,
 			      unsigned long irqflags, const char *devname,
 			      void *dev_id);
-int bind_virq_to_irq(unsigned int virq, unsigned int cpu);
+int bind_virq_to_irq(unsigned int virq, unsigned int cpu, bool percpu);
 int bind_virq_to_irqhandler(unsigned int virq, unsigned int cpu,
 			    irq_handler_t handler,
 			    unsigned long irqflags, const char *devname,