[ 048/115] Drivers: hv: vmbus: Fix a bug in hv_need_to_signal()

[Greg Kroah-Hartman]

3.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>

commit 288fa3e022eb85fa151e0f9bcd15caeb81679af6 upstream.

As part of updating the vmbus protocol, the function hv_need_to_signal()
was introduced. This functions helps optimize signalling from guest to
host. The newly added memory barrier is needed to ensure that we correctly
decide when to signal the host.

Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Reviewed-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Reported-by: Olaf Hering <olh@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/hv/ring_buffer.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -71,6 +71,7 @@ u32 hv_end_read(struct hv_ring_buffer_in
 
 static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
 {
+	smp_mb();
 	if (rbi->ring_buffer->interrupt_mask)
 		return false;
 


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