linux-kernel - [PATCH 1/1] Drivers: hv: vmbus: Fix a bug in hv_need_to

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Date:	Fri, 29 Mar 2013 14:30:38 -0700
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	jasowang@...hat.com
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Stable <stable@...r.kernel.org> (V3.8+)
Subject: [PATCH 1/1] 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@...rosoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>
Reported-by: Olaf Hering <olh@...e.de>

Cc: Stable <stable@...r.kernel.org>  (V3.8+)
---
 drivers/hv/ring_buffer.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index cafa72f..d6fbb577 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;
 
-- 
1.7.4.1

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