[RFC PATCH] Check if the Hangcheck-timer TSC source is stable

[Michael Trimarchi]

Check if the TSC source is stable otherwise fail registration.

Signed-off-by: Michael Trimarchi <trimarchimichael@xxxxxxxx>

---
diff --git a/drivers/char/hangcheck-timer.c b/drivers/char/hangcheck-timer.c
index 712d9f2..910a77a 100644
--- a/drivers/char/hangcheck-timer.c
+++ b/drivers/char/hangcheck-timer.c
@@ -10,12 +10,12 @@
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public
  * License version 2 as published by the Free Software Foundation.
- * 
+ *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
- * 
+ *
  * You should have received a copy of the GNU General Public
  * License along with this program; if not, write to the
  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
@@ -64,14 +64,18 @@ static int hangcheck_dump_tasks;  /* Defaults to not dumping SysRQ T */
 module_param(hangcheck_tick, int, 0);
 MODULE_PARM_DESC(hangcheck_tick, "Timer delay.");
 module_param(hangcheck_margin, int, 0);
-MODULE_PARM_DESC(hangcheck_margin, "If the hangcheck timer has been delayed more than hangcheck_margin seconds, the driver will fire.");
+MODULE_PARM_DESC(hangcheck_margin, "If the hangcheck timer has been delayed"
+		 " more than hangcheck_margin seconds, the driver will fire.");
 module_param(hangcheck_reboot, int, 0);
-MODULE_PARM_DESC(hangcheck_reboot, "If nonzero, the machine will reboot when the timer margin is exceeded.");
+MODULE_PARM_DESC(hangcheck_reboot, "If nonzero, the machine will reboot"
+		 " when the timer margin is exceeded.");
 module_param(hangcheck_dump_tasks, int, 0);
-MODULE_PARM_DESC(hangcheck_dump_tasks, "If nonzero, the machine will dump the system task state when the timer margin is exceeded.");
+MODULE_PARM_DESC(hangcheck_dump_tasks, "If nonzero, the machine will dump"
+		 " the system task state when the timer margin is exceeded.");
 
 MODULE_AUTHOR("Oracle");
-MODULE_DESCRIPTION("Hangcheck-timer detects when the system has gone out to lunch past a certain margin.");
+MODULE_DESCRIPTION("Hangcheck-timer detects when the system has gone"
+		   " out to lunch past a certain margin.");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(VERSION_STR);
 
@@ -81,7 +85,7 @@ MODULE_VERSION(VERSION_STR);
 static int __init hangcheck_parse_tick(char *str)
 {
 	int par;
-	if (get_option(&str,&par))
+	if (get_option(&str, &par))
 		hangcheck_tick = par;
 	return 1;
 }
@@ -89,7 +93,7 @@ static int __init hangcheck_parse_tick(char *str)
 static int __init hangcheck_parse_margin(char *str)
 {
 	int par;
-	if (get_option(&str,&par))
+	if (get_option(&str, &par))
 		hangcheck_margin = par;
 	return 1;
 }
@@ -97,7 +101,7 @@ static int __init hangcheck_parse_margin(char *str)
 static int __init hangcheck_parse_reboot(char *str)
 {
 	int par;
-	if (get_option(&str,&par))
+	if (get_option(&str, &par))
 		hangcheck_reboot = par;
 	return 1;
 }
@@ -105,7 +109,7 @@ static int __init hangcheck_parse_reboot(char *str)
 static int __init hangcheck_parse_dump_tasks(char *str)
 {
 	int par;
-	if (get_option(&str,&par))
+	if (get_option(&str, &par))
 		hangcheck_dump_tasks = par;
 	return 1;
 }
@@ -151,8 +155,10 @@ static void hangcheck_fire(unsigned long data)
 
 	if (cur_tsc > hangcheck_tsc)
 		tsc_diff = cur_tsc - hangcheck_tsc;
-	else
-		tsc_diff = (cur_tsc + (~0ULL - hangcheck_tsc)); /* or something */
+	else {
+		/* or samenthing */
+		tsc_diff = (cur_tsc + (~0ULL - hangcheck_tsc));
+	}
 
 	if (tsc_diff > hangcheck_tsc_margin) {
 		if (hangcheck_dump_tasks) {
@@ -172,15 +178,21 @@ static void hangcheck_fire(unsigned long data)
 	hangcheck_tsc = monotonic_clock();
 }
 
-
 static int __init hangcheck_init(void)
 {
-	printk("Hangcheck: starting hangcheck timer %s (tick is %d seconds, margin is %d seconds).\n",
+	printk(KERN_INFO "Hangcheck: starting hangcheck timer %s"
+			 " (tick is %d seconds, margin is %d seconds).\n",
 	       VERSION_STR, hangcheck_tick, hangcheck_margin);
-#if defined (HAVE_MONOTONIC)
-	printk("Hangcheck: Using monotonic_clock().\n");
+#if defined(HAVE_MONOTONIC)
+	printk(KERN_INFO "Hangcheck: Using monotonic_clock().\n");
 #else
-	printk("Hangcheck: Using get_cycles().\n");
+	if (!check_tsc_unstable())
+		printk(KERN_INFO "Hangcheck: Using get_cycles().\n");
+	else {
+		printk(KERN_ERR "Handcheck: Failed to register"
+		       " (Unstable TSC).\n");
+		return -ENODEV;
+	}
 #endif  /* HAVE_MONOTONIC */
 	hangcheck_tsc_margin =
 		(unsigned long long)(hangcheck_margin + hangcheck_tick);
@@ -196,7 +208,7 @@ static int __init hangcheck_init(void)
 static void __exit hangcheck_exit(void)
 {
 	del_timer_sync(&hangcheck_ticktock);
-        printk("Hangcheck: Stopped hangcheck timer.\n");
+	printk(KERN_INFO "Hangcheck: Stopped hangcheck timer.\n");
 }
 
 module_init(hangcheck_init);