xen: handle events as edge-triggered

commit dffe2e1e1a1ddb566a76266136c312801c66dcf7 upstream.

Xen events are logically edge triggered, as Xen only calls the event
upcall when an event is newly set, but not continuously as it remains set.
As a result, use handle_edge_irq rather than handle_level_irq.

This has the important side-effect of fixing a long-standing bug of
events getting lost if:
 - an event's interrupt handler is running
 - the event is migrated to a different vcpu
 - the event is re-triggered

The most noticable symptom of these lost events is occasional lockups
of blkfront.

Many thanks to Tom Kopec and Daniel Stodden in tracking this down.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Tom Kopec <tek@acm.org>
Cc: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 28f133ae76add51719aadbfc1b1f76f3da82bf27..cc72dad34ded77f8427898323f38f7ac0fddb566 100644 (file)
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -363,7 +363,7 @@ int bind_evtchn_to_irq(unsigned int evtchn)
                irq = find_unbound_irq();
 
                set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
-                                             handle_level_irq, "event");
+                                             handle_edge_irq, "event");
 
                evtchn_to_irq[evtchn] = irq;
                irq_info[irq] = mk_evtchn_info(evtchn);