locking/lockdep: Avoid triggering hardlockup from debug_show_all_locks()

debug_show_all_locks() iterates all tasks and print held locks whole
holding tasklist_lock.  This can take a while on a slow console device
and may end up triggering NMI hardlockup detector if someone else ends
up waiting for tasklist_lock.

Touch the NMI watchdog while printing the held locks to avoid
spuriously triggering the hardlockup detector.

Change-Id: I8ed50849c4464de1e2936d75b945e568a6090561
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@fb.com
Link: http://lkml.kernel.org/r/20180122220055.GB1771050@devbig577.frc2.facebook.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/lockdep.c

@@ -45,6 +45,7 @@
 #include <linux/bitops.h>
 #include <linux/gfp.h>
 #include <linux/kmemcheck.h>
+#include <linux/nmi.h>
 
 #include <asm/sections.h>
 
@@ -4163,6 +4164,7 @@ retry:
 		if (!unlock)
 			if (read_trylock(&tasklist_lock))
 				unlock = 1;
+		touch_nmi_watchdog();
 	} while_each_thread(g, p);
 
 	printk("\n");