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    Subject[PATCH 5.4 4/4] xen/events: reset active flag for lateeoi events later
    Date
    From: Juergen Gross <jgross@suse.com>

    commit 3de218ff39b9e3f0d453fe3154f12a174de44b25 upstream.

    In order to avoid a race condition for user events when changing
    cpu affinity reset the active flag only when EOI-ing the event.

    This is working fine as all user events are lateeoi events. Note that
    lateeoi_ack_mask_dynirq() is not modified as there is no explicit call
    to xen_irq_lateeoi() expected later.

    Cc: stable@vger.kernel.org
    Reported-by: Julien Grall <julien@xen.org>
    Fixes: b6622798bc50b62 ("xen/events: avoid handling the same event on two cpus at the same time")
    Tested-by: Julien Grall <julien@xen.org>
    Signed-off-by: Juergen Gross <jgross@suse.com>
    Reviewed-by: Boris Ostrovsky <boris.ostrvsky@oracle.com>
    Link: https://lore.kernel.org/r/20210623130913.9405-1-jgross@suse.com
    Signed-off-by: Juergen Gross <jgross@suse.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/xen/events/events_base.c | 23 +++++++++++++++++++----
    1 file changed, 19 insertions(+), 4 deletions(-)

    --- a/drivers/xen/events/events_base.c
    +++ b/drivers/xen/events/events_base.c
    @@ -525,6 +525,9 @@ static void xen_irq_lateeoi_locked(struc
    }

    info->eoi_time = 0;
    +
    + /* is_active hasn't been reset yet, do it now. */
    + smp_store_release(&info->is_active, 0);
    do_unmask(info, EVT_MASK_REASON_EOI_PENDING);
    }

    @@ -1781,10 +1784,22 @@ static void lateeoi_ack_dynirq(struct ir
    struct irq_info *info = info_for_irq(data->irq);
    evtchn_port_t evtchn = info ? info->evtchn : 0;

    - if (VALID_EVTCHN(evtchn)) {
    - do_mask(info, EVT_MASK_REASON_EOI_PENDING);
    - ack_dynirq(data);
    - }
    + if (!VALID_EVTCHN(evtchn))
    + return;
    +
    + do_mask(info, EVT_MASK_REASON_EOI_PENDING);
    +
    + if (unlikely(irqd_is_setaffinity_pending(data)) &&
    + likely(!irqd_irq_disabled(data))) {
    + do_mask(info, EVT_MASK_REASON_TEMPORARY);
    +
    + clear_evtchn(evtchn);
    +
    + irq_move_masked_irq(data);
    +
    + do_unmask(info, EVT_MASK_REASON_TEMPORARY);
    + } else
    + clear_evtchn(evtchn);
    }

    static void lateeoi_mask_ack_dynirq(struct irq_data *data)

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