[PATCH 1/4] hv: add helpers to handle hv_util device state

[Olaf Hering <olaf@aepfle.de>]

The callbacks in kvp, vss and fcopy code are called the main thread and
also 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>
---
 drivers/hv/hyperv_vmbus.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 3d70e36..6c03925 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -780,4 +780,16 @@ 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 */