[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 <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 42 insertions, 19 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index ea097dddc44f..7e1160dde5e7 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -132,6 +132,7 @@ struct lock_list {
         struct list_head                entry;
         struct lock_class               *class;
         struct stack_trace              trace;
+        int                             distance;
 };
 
 /*
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 2d616f4d853c..592c576d77a7 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -490,7 +490,7 @@ static void print_lock_dependencies(struct lock_class *class, int depth)
  * 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;
         /*
@@ -502,6 +502,7 @@ static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
                 return 0;
 
         entry->class = this;
+        entry->distance = distance;
         if (!save_trace(&entry->trace))
                 return 0;
 
@@ -906,7 +907,7 @@ check_deadlock(struct task_struct *curr, struct held_lock *next,
  */
 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;
@@ -984,8 +985,11 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
          *  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;
+                }
         }
 
         /*
@@ -993,12 +997,13 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
          * 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;
 
@@ -1046,13 +1051,14 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
                 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,
@@ -2779,4 +2785,3 @@ void debug_show_held_locks(struct task_struct *task)
 }
 
 EXPORT_SYMBOL_GPL(debug_show_held_locks);
-
diff --git a/kernel/lockdep_proc.c b/kernel/lockdep_proc.c
index b554b40a4aa6..57a547a2da3f 100644
--- a/kernel/lockdep_proc.c
+++ b/kernel/lockdep_proc.c
@@ -77,12 +77,29 @@ static unsigned long count_backward_deps(struct lock_class *class)
         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
@@ -97,16 +114,16 @@ static int l_show(struct seq_file *m, void *v)
         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");