watchdog: Add comments to explain the watchdog_disabled variable

The watchdog_disabled flag is a bit cryptic. However it's
usefulness is multifold. Uses are:

 1. Check if smpboot_register_percpu_thread function passed.

 2. Makes sure that user enables and disables the watchdog in
    sequence i.e. enable watchdog->disable watchdog->enable watchdog
    Unlike enable watchdog->enable watchdog which is wrong.

Signed-off-by: anish kumar <anish198519851985@gmail.com>
[small text cleanups]
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: chuansheng.liu@intel.com
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1363113848-18344-1-git-send-email-dzickus@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/watchdog.c

@@ -517,6 +517,11 @@ int proc_dowatchdog(struct ctl_table *table, int write,
 		return ret;
 
 	set_sample_period();
+	/*
+	 * Watchdog threads shouldn't be enabled if they are
+	 * disabled. The 'watchdog_disabled' variable check in
+	 * watchdog_*_all_cpus() function takes care of this.
+	 */
 	if (watchdog_enabled && watchdog_thresh)
 		watchdog_enable_all_cpus();
 	else