[PATCH 4.9 021/130] xen: add error handling for xenbus_printf

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Zhouyang Jia <jiazhouyang09@xxxxxxxxx>

[ Upstream commit 84c029a73327cef571eaa61c7d6e67e8031b52ec ]

When xenbus_printf fails, the lack of error-handling code may
cause unexpected results.

This patch adds error-handling code after calling xenbus_printf.

Signed-off-by: Zhouyang Jia <jiazhouyang09@xxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/xen/manage.c |   18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -291,8 +291,15 @@ static void sysrq_handler(struct xenbus_
 		return;
 	}
 
-	if (sysrq_key != '\0')
-		xenbus_printf(xbt, "control", "sysrq", "%c", '\0');
+	if (sysrq_key != '\0') {
+		err = xenbus_printf(xbt, "control", "sysrq", "%c", '\0');
+		if (err) {
+			pr_err("%s: Error %d writing sysrq in control/sysrq\n",
+			       __func__, err);
+			xenbus_transaction_end(xbt, 1);
+			return;
+		}
+	}
 
 	err = xenbus_transaction_end(xbt, 0);
 	if (err == -EAGAIN)
@@ -344,7 +351,12 @@ static int setup_shutdown_watcher(void)
 			continue;
 		snprintf(node, FEATURE_PATH_SIZE, "feature-%s",
 			 shutdown_handlers[idx].command);
-		xenbus_printf(XBT_NIL, "control", node, "%u", 1);
+		err = xenbus_printf(XBT_NIL, "control", node, "%u", 1);
+		if (err) {
+			pr_err("%s: Error %d writing %s\n", __func__,
+				err, node);
+			return err;
+		}
 	}
 
 	return 0;