From: Miroslav Rezanina <mrezanin@redhat.com>
Date: Thu, 11 Mar 2010 09:47:11 -0500
Subject: [misc] xen: fix migration using xen-vnif in smp hvm guest
Message-id: <1333479563.238831268300831083.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com>
Patchwork-id: 23545
O-Subject: [RHEL5.5 XEN PATCH] xen migration fails when a full virt guest uses
	the xen-vnif driver
Bugzilla: 555910
RH-Acked-by: Don Dutile <ddutile@redhat.com>
RH-Acked-by: Jarod Wilson <jarod@redhat.com>
RH-Acked-by: Andrew Jones <drjones@redhat.com>

BZ 555910 (https://bugzilla.redhat.com/show_bug.cgi?id=555910) xen migration fails when a full virt guest uses the xen-vnif driver

Brewbuild: https://brewweb.devel.redhat.com/taskinfo?taskID=2313996

When a guest is using the xen-vnif drivers as a full-virt guest under xen. The guest
will completely freeze when you save-restore/migrate the guest. This is caused by deadlock
between xen_suspend kernel thread and the xenbus_thread kernel thread.

Upstream kernel do suspend stuff after freezing processes to prevent daedlock. Our
code call xenbus_suspend before handling preempting. When we move xenbus_suspend
after preempt_disable deadlock does not occur.

Patch:
------

Signed-off-by: Jarod Wilson <jarod@redhat.com>

diff --git a/drivers/xen/core/reboot.c b/drivers/xen/core/reboot.c
index 929c590..060d4e5 100644
--- a/drivers/xen/core/reboot.c
+++ b/drivers/xen/core/reboot.c
@@ -183,10 +183,10 @@ static int __do_suspend(void *ignore)
 	if (err)
 		return err;
 
-	xenbus_suspend();
-
 	preempt_disable();
 
+	xenbus_suspend();
+
 	mm_pin_all();
 	local_irq_disable();
 	preempt_enable();