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    Subject[34-longterm 030/260] xen: handle events as edge-triggered
    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: Paul Gortmaker <>
    drivers/xen/events.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/drivers/xen/events.c b/drivers/xen/events.c
    index 28f133a..cc72dad 100644
    --- 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);

     \ /
      Last update: 2011-01-02 08:25    [W:0.021 / U:48.048 seconds]
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