[Xen-devel] [PATCH] xen/events/fifo: Consume unprocessed events when a CPU dies

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

When a CPU is offlined, there may be unprocessed events on a port for
that CPU.  If the port is subsequently reused on a different CPU, it
could be in an unexpected state with the link bit set, resulting in
interrupts being missed. Fix this by consuming any unprocessed events
for a particular CPU when that CPU dies.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
 drivers/xen/events/events_fifo.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 417415d..1dd0ba12 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -281,7 +281,8 @@ static void handle_irq_for_port(unsigned port)
 
 static void consume_one_event(unsigned cpu,
                              struct evtchn_fifo_control_block *control_block,
-                             unsigned priority, unsigned long *ready)
+                             unsigned priority, unsigned long *ready,
+                             bool drop)
 {
        struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
        uint32_t head;
@@ -313,13 +314,17 @@ static void consume_one_event(unsigned cpu,
        if (head == 0)
                clear_bit(priority, ready);
 
-       if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port))
-               handle_irq_for_port(port);
+       if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port)) {
+               if (unlikely(drop))
+                       pr_warn("Dropping pending event for port %u\n", port);
+               else
+                       handle_irq_for_port(port);
+       }
 
        q->head[priority] = head;
 }
 
-static void evtchn_fifo_handle_events(unsigned cpu)
+static void __evtchn_fifo_handle_events(unsigned cpu, bool drop)
 {
        struct evtchn_fifo_control_block *control_block;
        unsigned long ready;
@@ -331,11 +336,16 @@ static void evtchn_fifo_handle_events(unsigned cpu)
 
        while (ready) {
                q = find_first_bit(&ready, EVTCHN_FIFO_MAX_QUEUES);
-               consume_one_event(cpu, control_block, q, &ready);
+               consume_one_event(cpu, control_block, q, &ready, drop);
                ready |= xchg(&control_block->ready, 0);
        }
 }
 
+static void evtchn_fifo_handle_events(unsigned cpu)
+{
+       __evtchn_fifo_handle_events(cpu, false);
+}
+
 static void evtchn_fifo_resume(void)
 {
        unsigned cpu;
@@ -420,6 +430,9 @@ static int evtchn_fifo_cpu_notification(struct 
notifier_block *self,
                if (!per_cpu(cpu_control_block, cpu))
                        ret = evtchn_fifo_alloc_control_block(cpu);
                break;
+       case CPU_DEAD:
+               __evtchn_fifo_handle_events(cpu, true);
+               break;
        default:
                break;
        }
-- 
2.1.0


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