On Wed, Nov 28, 2018 at 03:43:20PM -0800, Bart Van Assche wrote:
> Instead of abandoning elements of list_entries[] that are no longer in
> use, make alloc_list_entry() reuse array elements that have been freed.
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 43327a1dd488..01e55fca7c2c 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -183,6 +183,11 @@ static inline void lockdep_copy_map(struct lockdep_map
> *to,
> struct lock_list {
> /* Entry in locks_after or locks_before. */
> struct list_head lock_order_entry;
> + /*
> + * Entry in all_list_entries when in use and entry in
> + * free_list_entries when not in use.
> + */
> + struct list_head alloc_entry;
> struct lock_class *class;
> struct lock_class *links_to;
> struct stack_trace trace;
> +static LIST_HEAD(all_list_entries);
> +static LIST_HEAD(free_list_entries);
>
> @@ -862,7 +867,10 @@ register_lock_class(struct lockdep_map *lock, unsigned
> int subclass, int force)
> */
> static struct lock_list *alloc_list_entry(void)
> {
> - if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) {
> + struct lock_list *e = list_first_entry_or_null(&free_list_entries,
> + typeof(*e), alloc_entry);
> +
> + if (!e) {
> if (!debug_locks_off_graph_unlock())
> return NULL;
>
> @@ -870,7 +878,8 @@ static struct lock_list *alloc_list_entry(void)
> dump_stack();
> return NULL;
> }
> - return list_entries + nr_list_entries++;
> + list_move_tail(&e->alloc_entry, &all_list_entries);
> + return e;
> }
> @@ -4235,19 +4244,19 @@ static void zap_class(struct list_head
> *zapped_classes,
> struct lock_class *class)
> {
> struct lock_class *links_to;
> + struct lock_list *entry, *tmp;
>
> /*
> * Remove all dependencies this lock is
> * involved in:
> */
> + list_for_each_entry_safe(entry, tmp, &all_list_entries, alloc_entry) {
> if (entry->class != class && entry->links_to != class)
> continue;
> links_to = entry->links_to;
> WARN_ON_ONCE(entry->class == links_to);
> list_del_rcu(&entry->lock_order_entry);
> + list_move(&entry->alloc_entry, &free_list_entries);
> entry->class = NULL;
> entry->links_to = NULL;
> check_free_class(zapped_classes, class);
Hurm.. I'm confused here.
The reason you cannot re-use lock_order_entry for the free list is
because list_del_rcu(), right? But if so, then what ensures the
list_entry is not re-used before it's grace-period?
