[RFC tip/locking v2 06/13] lockdep: Adjust check_redundant() for recursive read change

[Boqun Feng]

As we have four kinds of dependencies now, check_redundant() should only
report redundant if we have a dependency path which is equal or
_stronger_ than the current dependency. For example if check_prev_add()
we have:

        prev->read == 2 && next->read != 2

, we should only report redundant if we find a path like:

        prev--(RN)-->....--(*N)-->next

and if we have:

        prev->read == 2 && next->read == 2

, we could report redundant if we find a path like:

        prev--(RN)-->....--(*N)-->next

or

        prev--(RN)-->....--(*R)-->next

To do so, we need to pass the recursive-read status of next into
check_redundant(). This patch changes the parameter of check_redundant()
and the match function to achieve this.

Signed-off-by: Boqun Feng <boqun.f...@gmail.com>
---
 kernel/locking/lockdep.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 3c43af353ea0..d9959f25247a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1337,9 +1337,12 @@ print_circular_bug_header(struct lock_list *entry, 
unsigned int depth,
        return 0;
 }
 
-static inline int class_equal(struct lock_list *entry, void *data)
+static inline int hlock_equal(struct lock_list *entry, void *data)
 {
-       return entry->class == 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,
@@ -1473,14 +1476,14 @@ check_noncircular(struct lock_list *root, struct 
lock_class *target,
 }
 
 static noinline enum bfs_result
-check_redundant(struct lock_list *root, struct lock_class *target,
+check_redundant(struct lock_list *root, struct held_lock *target,
                struct lock_list **target_entry)
 {
        enum bfs_result result;
 
        debug_atomic_inc(nr_redundant_checks);
 
-       result = __bfs_forwards(root, target, class_equal, target_entry);
+       result = __bfs_forwards(root, target, hlock_equal, target_entry);
 
        return result;
 }
@@ -2047,7 +2050,7 @@ check_prev_add(struct task_struct *curr, struct held_lock 
*prev,
         * Is the <prev> -> <next> link redundant?
         */
        bfs_init_root(&this, prev);
-       ret = check_redundant(&this, hlock_class(next), &target_entry);
+       ret = check_redundant(&this, next, &target_entry);
        if (ret == BFS_RMATCH) {
                debug_atomic_inc(nr_redundant);
                return 2;
-- 
2.14.1