[RFC tip/locking v2 07/13] lockdep: Support deadlock detection for recursive read in check_noncircular()

[Boqun Feng <boqun.feng@gmail.com>]

Currently, lockdep only has limit support for deadlock detection for
recursive read locks.

The basic idea of the detection is:

Since we make __bfs() able to traverse only the strong dependency paths,
so we report a circular deadlock if we could find a circle of a strong
dependency path.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/locking/lockdep.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index d9959f25247a..8a09b1a02342 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1345,6 +1345,14 @@ static inline int hlock_equal(struct lock_list *entry, void *data)
 	       (hlock->read == 2 || !entry->is_rr);
 }
 
+static inline int hlock_conflict(struct lock_list *entry, void *data)
+{
+	struct held_lock *hlock = (struct held_lock *)data;
+
+	return hlock_class(hlock) == entry->class &&
+	       (hlock->read != 2 || !entry->is_rr);
+}
+
 static noinline int print_circular_bug(struct lock_list *this,
 				struct lock_list *target,
 				struct held_lock *check_src,
@@ -1459,18 +1467,18 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
 }
 
 /*
- * Prove that the dependency graph starting at <entry> can not
+ * Prove that the dependency graph starting at <root> can not
  * lead to <target>. Print an error and return BFS_RMATCH if it does.
  */
 static noinline enum bfs_result
-check_noncircular(struct lock_list *root, struct lock_class *target,
+check_noncircular(struct lock_list *root, struct held_lock *target,
 		  struct lock_list **target_entry)
 {
 	enum bfs_result result;
 
 	debug_atomic_inc(nr_cyclic_checks);
 
-	result = __bfs_forwards(root, target, class_equal, target_entry);
+	result = __bfs_forwards(root, target, hlock_conflict, target_entry);
 
 	return result;
 }
-- 
2.14.1