lockdep/waitqueues: Add better annotation

-> #2 (&tty->write_wait){-.-...}:

is a lot more informative than:

-> #2 (key#19){-.....}:

Signed-off-by: Peter Zijlstra <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

include/linux/wait.h

···
 #define __WAIT_BIT_KEY_INITIALIZER(word, bit)				\
 	{ .flags = word, .bit_nr = bit, }
 
-extern void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *);
+extern void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *);
 
 #define init_waitqueue_head(q)				\
 	do {						\
 		static struct lock_class_key __key;	\
 							\
-		__init_waitqueue_head((q), &__key);	\
+		__init_waitqueue_head((q), #q, &__key);	\
 	} while (0)
 
 #ifdef CONFIG_LOCKDEP

kernel/wait.c

···
 #include <linux/wait.h>
 #include <linux/hash.h>
 
-void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *key)
+void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
 {
 	spin_lock_init(&q->lock);
-	lockdep_set_class(&q->lock, key);
+	lockdep_set_class_and_name(&q->lock, key, name);
 	INIT_LIST_HEAD(&q->task_list);
 }