linux-kernel - [PATCH v2] Softdog enhancement to optionally invoke panic instead of reboot on timer expiry

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Message-ID: <20110125000352.0be09450@linux.vnet.ibm.com>
Date:	Tue, 25 Jan 2011 00:03:52 +0530
From:	Anithra P Janakiraman <anithra@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	dave@...ux.vnet.ibm.com, xiyou.wangcong@...il.com,
	sugaken.r3@...il.com, alan@...rguk.ukuu.org.uk,
	srikar@...ux.vnet.ibm.com, suzuki@...ibm.com,
	vatsa@...ux.vnet.ibm.com, ananth@...ibm.com
Subject: [PATCH v2] Softdog enhancement to optionally invoke panic instead
 of reboot on timer expiry


Hi,

We currently have no way of determining the reason for failure when a
softdog timeout occurs. We use softdog to watch for critical application
failures, and at the minimum a snapshot of the system would help to
determine the cause. In such a scenario the application could fail but
there isn't a softlockup as such, hence the detect softlockup feature
does not help.
The patch below adds a module parameter soft_panic which when set to
1 causes softdog to invoke panic instead of reboot when the softdog
timer expires. By invoking panic we execute kdump if it is configured
and the vmcore generated by kdump should provide atleast a minimal idea
of the reason for failure.

Based on an original patch by Ken Sugawara <sugaken.r3@...il.com>
Signed-off-by: Anithra P J <anithra@...ux.vnet.ibm.com>
---
 drivers/watchdog/softdog.c |   18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

Index: linux-2.6.38-rc1/drivers/watchdog/softdog.c
===================================================================
--- linux-2.6.38-rc1.orig/drivers/watchdog/softdog.c
+++ linux-2.6.38-rc1/drivers/watchdog/softdog.c
@@ -48,6 +48,7 @@
 #include <linux/init.h>
 #include <linux/jiffies.h>
 #include <linux/uaccess.h>
+#include <linux/kernel.h>
 
 #define PFX "SoftDog: "
 
@@ -75,6 +76,13 @@
 	"Softdog action, set to 1 to ignore reboots, 0 to reboot "
 					"(default depends on ONLY_TESTING)");
 
+
+static int soft_panic;
+
+module_param(soft_panic, int, 0);
+MODULE_PARM_DESC(soft_panic,
+	"Softdog action, set to 1 to panic, 0 to reboot (default 0)");
+
 /*
  *	Our timer
  */
@@ -98,7 +106,10 @@
 
 	if (soft_noboot)
 		printk(KERN_CRIT PFX "Triggered - Reboot ignored.\n");
-	else {
+	else if (soft_panic) {
+		printk(KERN_CRIT PFX "Initiating panic.\n");
+		panic("Software Watchdog Timer expired.");
+	} else {
 		printk(KERN_CRIT PFX "Initiating system reboot.\n");
 		emergency_restart();
 		printk(KERN_CRIT PFX "Reboot didn't ?????\n");
@@ -267,7 +278,8 @@
 };
 
 static char banner[] __initdata = KERN_INFO "Software Watchdog Timer: 0.07 "
-	"initialized. soft_noboot=%d soft_margin=%d sec (nowayout= %d)\n";
+	"initialized. soft_noboot=%d soft_margin=%d sec soft_panic=%d "
+	"(nowayout= %d)\n";
 
 static int __init watchdog_init(void)
 {
@@ -298,7 +310,7 @@
 		return ret;
 	}
 
-	printk(banner, soft_noboot, soft_margin, nowayout);
+	printk(banner, soft_noboot, soft_margin, soft_panic, nowayout);
 
 	return 0;
 }



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