From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Fri, 26 Feb 2016 23:13:18 +0000 (-0800)
Subject: Drivers: hv: vmbus: avoid unneeded compiler optimizations in vmbus_wait_for_unload()
X-Git-Tag: Ubuntu-snapdragon-4.4.0-1029.32~2783
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=9ab3d057309d72111d54043de842d1f5a576befa;p=mirror_ubuntu-zesty-kernel.git

Drivers: hv: vmbus: avoid unneeded compiler optimizations in vmbus_wait_for_unload()

BugLink: http://bugs.launchpad.net/bugs/1541585

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@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Radim Kr.má<rkrcmar@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit d452ab7b4c65dfcaee88a0d6866eeeb98a3d1884)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 73a17be1f340..38b682bab85a 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -605,7 +605,7 @@ 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;
 		}