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 30e04672ba65c2daa1e923ce8bc3aadbafd404b8..50cfdb02390b63517ed1813479819ed0fcc2d660 100644 (file)
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -362,7 +362,7 @@ 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);