From: cl349@firebug.cl.cam.ac.uk <cl349@firebug.cl.cam.ac.uk>
Date: Tue, 13 Sep 2005 21:24:03 +0000 (+0000)
Subject: Don't cause watch fire deadlock by unconditionally rewriting the sysrq node.
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~16806^2~26
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/%22/%22http:/www.example.com/cgi/%22?a=commitdiff_plain;h=5333aa48f3f8799e9d5233fd2603b6be7a046b7b;p=xen.git

Don't cause watch fire deadlock by unconditionally rewriting the sysrq node.
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
---

diff --git a/linux-2.6-xen-sparse/arch/xen/kernel/reboot.c b/linux-2.6-xen-sparse/arch/xen/kernel/reboot.c
index 2358970468..b6608cef49 100644
--- a/linux-2.6-xen-sparse/arch/xen/kernel/reboot.c
+++ b/linux-2.6-xen-sparse/arch/xen/kernel/reboot.c
@@ -355,16 +355,26 @@ static void shutdown_handler(struct xenbus_watch *watch, const char *node)
 static void sysrq_handler(struct xenbus_watch *watch, const char *node)
 {
     char sysrq_key = '\0';
-    
+    int err;
+
+ again:
+    err = xenbus_transaction_start("control");
+    if (err)
+	return;
     if (!xenbus_scanf("control", "sysrq", "%c", &sysrq_key)) {
         printk(KERN_ERR "Unable to read sysrq code in control/sysrq\n");
-        return;
+	xenbus_transaction_end(1);
+	return;
     }
 
-    xenbus_printf("control", "sysrq", "%c", '\0');
+    if (sysrq_key != '\0')
+	xenbus_printf("control", "sysrq", "%c", '\0');
 
-    if (sysrq_key != '\0') {
+    err = xenbus_transaction_end(0);
+    if (err == -ETIMEDOUT)
+	goto again;
 
+    if (sysrq_key != '\0') {
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,0)
         handle_sysrq(sysrq_key, NULL, NULL);
 #else