[RFC tip/locking/lockdep v5 06/17] lockdep: Support deadlock detection for recursive read in check_noncircular()

Boqun Feng
2018-02-22T07:06:16Z

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 | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 07bcfaac6fe2..e1be088a34c4 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1343,6 +1343,14 @@ static inline int class_equal(struct lock_list *entry, void *data)
return entry->class == data;
}

+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,
@@ -1455,18 +1463,18 @@ 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;
}
@@ -1994,7 +2002,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
* keep the stackframe size of the recursive functions low:
*/
bfs_init_root(&this, next);
- ret = check_noncircular(&this, hlock_class(prev), &target_entry);
+ ret = check_noncircular(&this, prev, &target_entry);
if (unlikely(ret == BFS_RMATCH)) {
if (!trace->entries) {
/*
--
2.16.1