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Subject[RFC tip/locking v2 06/13] lockdep: Adjust check_redundant() for recursive read change
Date
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.feng@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
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