[PATCH] detect soft lockups

This patch adds a new kernel debug feature: CONFIG_DETECT_SOFTLOCKUP.

When enabled then per-CPU watchdog threads are started, which try to run
once per second.  If they get delayed for more than 10 seconds then a
callback from the timer interrupt detects this condition and prints out a
warning message and a stack dump (once per lockup incident).  The feature
is otherwise non-intrusive, it doesnt try to unlock the box in any way, it
only gets the debug info out, automatically, and on all CPUs affected by
the lockup.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-Off-By: Matthias Urlichs <smurf@smurf.noris.de>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/nmi.c

@@ -478,6 +478,11 @@ void touch_nmi_watchdog (void)
 	 */
 	for (i = 0; i < NR_CPUS; i++)
 		alert_counter[i] = 0;
+
+	/*
+	 * Tickle the softlockup detector too:
+	 */
+	touch_softlockup_watchdog();
 }
 
 extern void die_nmi(struct pt_regs *, const char *msg);

arch/i386/kernel/time.c

@@ -422,6 +422,7 @@ static int timer_resume(struct sys_device *dev)
 		last_timer->resume();
 	cur_timer = last_timer;
 	last_timer = NULL;
+	touch_softlockup_watchdog();
 	return 0;
 }