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>

2 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b6a56e37284c..d36619ead3ba 100644
--- a/include/linux/lockdep.h
+++ b/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
diff --git a/kernel/printk.c b/kernel/printk.c
index 1455a0d4eedd..6d087944e72a 100644
--- a/kernel/printk.c
+++ b/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;
                 }