[PATCH] lockdep: add graph depth information to /proc/lockdep

Generate locking graph information into /proc/lockdep, for lock hierarchy
documentation and visualization purposes.

sample output:

c089fd5c OPS: 138 FD: 14 BD: 1 --..: &tty->termios_mutex
-> [c07a3430] tty_ldisc_lock
-> [c07a37f0] &port_lock_key
-> [c07afdc0] &rq->rq_lock_key#2

The lock classes listed are all the first-hop lock dependencies that
lockdep has seen so far.

Signed-off-by: Ingo Molnar <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/lockdep.h

···
 	struct list_head		entry;
 	struct lock_class		*class;
 	struct stack_trace		trace;
+	int				distance;
 };
 
 /*

kernel/lockdep.c

···
  * Add a new dependency to the head of the list:
  */
 static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
-			    struct list_head *head, unsigned long ip)
+			    struct list_head *head, unsigned long ip, int distance)
 {
 	struct lock_list *entry;
 	/*
···
 		return 0;
 
 	entry->class = this;
+	entry->distance = distance;
 	if (!save_trace(&entry->trace))
 		return 0;
 
···
  */
 static int
 check_prev_add(struct task_struct *curr, struct held_lock *prev,
-	       struct held_lock *next)
+	       struct held_lock *next, int distance)
 {
 	struct lock_list *entry;
 	int ret;
···
 	 *  L2 added to its dependency list, due to the first chain.)
 	 */
 	list_for_each_entry(entry, &prev->class->locks_after, entry) {
-		if (entry->class == next->class)
+		if (entry->class == next->class) {
+			if (distance == 1)
+				entry->distance = 1;
 			return 2;
+		}
 	}
 
 	/*
···
 	 * to the previous lock's dependency list:
 	 */
 	ret = add_lock_to_list(prev->class, next->class,
-			       &prev->class->locks_after, next->acquire_ip);
+			       &prev->class->locks_after, next->acquire_ip, distance);
+
 	if (!ret)
 		return 0;
 
 	ret = add_lock_to_list(next->class, prev->class,
-			       &next->class->locks_before, next->acquire_ip);
+			       &next->class->locks_before, next->acquire_ip, distance);
 	if (!ret)
 		return 0;
 
···
 		goto out_bug;
 
 	for (;;) {
+		int distance = curr->lockdep_depth - depth + 1;
 		hlock = curr->held_locks + depth-1;
 		/*
 		 * Only non-recursive-read entries get new dependencies
 		 * added:
 		 */
 		if (hlock->read != 2) {
-			if (!check_prev_add(curr, hlock, next))
+			if (!check_prev_add(curr, hlock, next, distance))
 				return 0;
 			/*
 			 * Stop after the first non-trylock entry,
···
 }
 
 EXPORT_SYMBOL_GPL(debug_show_held_locks);
-

kernel/lockdep_proc.c

···
 	return ret;
 }
 
+static void print_name(struct seq_file *m, struct lock_class *class)
+{
+	char str[128];
+	const char *name = class->name;
+
+	if (!name) {
+		name = __get_key_name(class->key, str);
+		seq_printf(m, "%s", name);
+	} else{
+		seq_printf(m, "%s", name);
+		if (class->name_version > 1)
+			seq_printf(m, "#%d", class->name_version);
+		if (class->subclass)
+			seq_printf(m, "/%d", class->subclass);
+	}
+}
+
 static int l_show(struct seq_file *m, void *v)
 {
 	unsigned long nr_forward_deps, nr_backward_deps;
 	struct lock_class *class = m->private;
-	char str[128], c1, c2, c3, c4;
-	const char *name;
+	struct lock_list *entry;
+	char c1, c2, c3, c4;
 
 	seq_printf(m, "%p", class->key);
 #ifdef CONFIG_DEBUG_LOCKDEP
···
 	get_usage_chars(class, &c1, &c2, &c3, &c4);
 	seq_printf(m, " %c%c%c%c", c1, c2, c3, c4);
 
-	name = class->name;
-	if (!name) {
-		name = __get_key_name(class->key, str);
-		seq_printf(m, ": %s", name);
-	} else{
-		seq_printf(m, ": %s", name);
-		if (class->name_version > 1)
-			seq_printf(m, "#%d", class->name_version);
-		if (class->subclass)
-			seq_printf(m, "/%d", class->subclass);
+	seq_printf(m, ": ");
+	print_name(m, class);
+	seq_puts(m, "\n");
+
+	list_for_each_entry(entry, &class->locks_after, entry) {
+		if (entry->distance == 1) {
+			seq_printf(m, " -> [%p] ", entry->class);
+			print_name(m, entry->class);
+			seq_puts(m, "\n");
+		}
 	}
 	seq_puts(m, "\n");