linux-kernel - [PATCH 4/4] Drivers: hv: vmbus: avoid unneeded compiler optimizations in vmbus_wait_for

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Date:	Fri, 12 Feb 2016 16:42:50 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	devel@...uxdriverproject.org
Cc:	linux-kernel@...r.kernel.org,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Radim Krcmar <rkrcmar@...hat.com>,
	Cathy Avery <cavery@...hat.com>
Subject: [PATCH 4/4] Drivers: hv: vmbus: avoid unneeded compiler optimizations in vmbus_wait_for_unload()

Message header is modified by the hypervisor and we read it in a loop,
we need to prevent compilers from optimizing accesses. There are no such
optimizations at this moment, this is just a future proof.

Suggested-by: Radim Krcmar <rkrcmar@...hat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 drivers/hv/channel_mgmt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 1e43967..b10e8f74 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -520,7 +520,7 @@ static void vmbus_wait_for_unload(void)
 	bool unloaded = false;
 
 	while (1) {
-		if (msg->header.message_type == HVMSG_NONE) {
+		if (READ_ONCE(msg->header.message_type) == HVMSG_NONE) {
 			mdelay(10);
 			continue;
 		}
-- 
2.5.0