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Subject[003/129] xen: handle events as edge-triggered
2.6.35-stable review patch.  If anyone has any objections, please let us know.


From: Jeremy Fitzhardinge <>

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 <>
Cc: Tom Kopec <>
Cc: Daniel Stodden <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/xen/events.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -363,7 +363,7 @@ int bind_evtchn_to_irq(unsigned int evtc
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);

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