From 288fa3e022eb85fa151e0f9bcd15caeb81679af6 Mon Sep 17 00:00:00 2001
From: "K. Y. Srinivasan" <kys@microsoft.com>
Date: Fri, 29 Mar 2013 14:30:38 -0700
Subject: [PATCH] Drivers: hv: vmbus: Fix a bug in hv_need_to_signal()

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@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Reported-by: Olaf Hering <olh@suse.de>
Cc: Stable <stable@vger.kernel.org>  (V3.8+)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/hv/ring_buffer.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index cafa72ffdc30..d6fbb5772b8d 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -71,6 +71,7 @@ u32 hv_end_read(struct hv_ring_buffer_info *rbi)
 
 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;
 
-- 
2.20.1