[PATCH 2/5] hv: add helpers to handle hv_util device state

["K. Y. Srinivasan" <kys@microsoft.com>]

From: Olaf Hering <olaf@aepfle.de>

The callbacks in kvp, vss and fcopy code are called both from the main thread
as well as from interrupt context. If a state change is done by the main
thread it is not immediately seen by the interrupt. As a result the
state machine gets out of sync.

Force propagation of state changes via get/set helpers with a memory barrier.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
 drivers/hv/hyperv_vmbus.h |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 4b1eb6d..dee5798 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -780,4 +780,18 @@ enum hvutil_device_state {
 	HVUTIL_DEVICE_DYING,     /* driver unload is in progress */
 };
 
+static inline void hvutil_device_set_state(enum hvutil_device_state *p,
+					   enum hvutil_device_state s)
+{
+	*p = s;
+	wmb();
+}
+
+static inline enum hvutil_device_state
+hvutil_device_get_state(enum hvutil_device_state *p)
+{
+	rmb();
+	return *p;
+}
+
 #endif /* _HYPERV_VMBUS_H */
-- 
1.7.4.1