ftrace: fix locking

we can hold all cpu trace buffer locks at once - put each into a
separate lock class.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 29a7ea5..b040835 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -56,6 +56,7 @@
 	struct list_head	trace_pages;
 	atomic_t		disabled;
 	spinlock_t		lock;
+	struct lock_class_key	lock_key;
 	cycle_t			time_offset;
 
 	/* these fields get copied into max-trace: */