From e91e84fa4cfeb67a9a096f1adaa1a1a692474724 Mon Sep 17 00:00:00 2001
From: Jason Wang <jasowang@redhat.com>
Date: Thu, 20 Jun 2013 12:58:57 +0800
Subject: [PATCH] drivers: hv: check interrupt mask before read_index

This patches add a read barriers to force the driver to check the interrupt mask
before read_index. Otherwise we may lost a kick to host.

Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by:  K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/hv/ring_buffer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 791f45dfc85d..26c93cf9f6be 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -75,6 +75,8 @@ static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
 	if (rbi->ring_buffer->interrupt_mask)
 		return false;
 
+	/* check interrupt_mask before read_index */
+	rmb();
 	/*
 	 * This is the only case we need to signal when the
 	 * ring transitions from being empty to non-empty.