printk, lockdep: Disable lock debugging on zap_locks()

zap_locks() is used by printk() in a last ditch effort to get data
out, clearly we cannot trust lock state after this so make it disable
lock debugging.

Also don't treat printk recursion through lockdep as a normal
recursion bug but try hard to get the lockdep splat out.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-kqxwmo4xz37e1s8w0xopvr0q@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/lockdep.h

@@ -343,6 +343,8 @@ extern void lockdep_trace_alloc(gfp_t mask);
 
 #define lockdep_assert_held(l)	WARN_ON(debug_locks && !lockdep_is_held(l))
 
+#define lockdep_recursing(tsk)	((tsk)->lockdep_recursion)
+
 #else /* !LOCKDEP */
 
 static inline void lockdep_off(void)
@@ -392,6 +394,8 @@ struct lock_class_key { };
 
 #define lockdep_assert_held(l)			do { } while (0)
 
+#define lockdep_recursing(tsk)			(0)
+
 #endif /* !LOCKDEP */
 
 #ifdef CONFIG_LOCK_STAT

kernel/printk.c

@@ -688,6 +688,7 @@ static void zap_locks(void)
 
 	oops_timestamp = jiffies;
 
+	debug_locks_off();
 	/* If a crash is occurring, make sure we can't deadlock */
 	raw_spin_lock_init(&logbuf_lock);
 	/* And make sure that we print immediately */
@@ -856,7 +857,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 		 * recursion and return - but flag the recursion so that
 		 * it can be printed at the next appropriate moment:
 		 */
-		if (!oops_in_progress) {
+		if (!oops_in_progress && !lockdep_recursing(current)) {
 			recursion_bug = 1;
 			goto out_restore_irqs;
 		}