lock_list::distance is always not greater than MAX_LOCKDEP_DEPTH (which is 48 right now), so a u16 will fit. This patch reduces the size of lock_list::distance to save space, so that we can introduce other fields to help detect recursive read lock deadlocks without increasing the size of lock_list structure.
Suggested-by: Peter Zijlstra <pet...@infradead.org> Signed-off-by: Boqun Feng <boqun.f...@gmail.com> --- include/linux/lockdep.h | 2 +- kernel/locking/lockdep.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 6fc77d4dbdcd..d2af32387aaa 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -186,7 +186,7 @@ struct lock_list { struct list_head entry; struct lock_class *class; struct stack_trace trace; - int distance; + u16 distance; /* * The parent field is used to implement breadth-first search, and the diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 14af2327b52a..1806060c88ce 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -859,7 +859,7 @@ static struct lock_list *alloc_list_entry(void) * Add a new dependency to the head of the list: */ static int add_lock_to_list(struct lock_class *this, struct list_head *head, - unsigned long ip, int distance, + unsigned long ip, u16 distance, struct stack_trace *trace) { struct lock_list *entry; @@ -1996,7 +1996,7 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) goto out_bug; for (;;) { - int distance = curr->lockdep_depth - depth + 1; + u16 distance = curr->lockdep_depth - depth + 1; hlock = curr->held_locks + depth - 1; /* -- 2.16.2