xen/events: reset active flag for lateeoi events later

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>

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 7bbfd58958bcc542049e5763bb1d4df1bcbcadb6..d7e361fb05482d43765243d222072a52441be0cf 100644 (file)
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -642,6 +642,9 @@ static void xen_irq_lateeoi_locked(struct irq_info *info, bool spurious)
        }
 
        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);
 }
 
@@ -811,6 +814,7 @@ static void xen_evtchn_close(evtchn_port_t port)
                BUG();
 }
 
+/* Not called for lateeoi events. */
 static void event_handler_exit(struct irq_info *info)
 {
        smp_store_release(&info->is_active, 0);
@@ -1883,7 +1887,12 @@ static void lateeoi_ack_dynirq(struct irq_data *data)
 
        if (VALID_EVTCHN(evtchn)) {
                do_mask(info, EVT_MASK_REASON_EOI_PENDING);
-               event_handler_exit(info);
+               /*
+                * Don't call event_handler_exit().
+                * Need to keep is_active non-zero in order to ignore re-raised
+                * events after cpu affinity changes while a lateeoi is pending.
+                */
+               clear_evtchn(evtchn);
        }
 }