[4.2.y-ckt stable] Patch "xen/events/fifo: Consume unprocessed events when a CPU dies" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xen/events/fifo: Consume unprocessed events when a CPU dies

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 97a45eb49a70bea5f7861dc854e15ae6a7fbd83a Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <ross.lagerwall at citrix.com>
Date: Fri, 19 Jun 2015 16:15:57 +0100
Subject: xen/events/fifo: Consume unprocessed events when a CPU dies

commit 3de88d622fd68bd4dbee0f80168218b23f798fd0 upstream.

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 at citrix.com>
Signed-off-by: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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 ed673e1..b14545e 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;
 	}
--
1.9.1