A weird KASAN problem that Zygo reported could have been easily caught
if we checked for basic things in our backref freeing code. We have two
methods of freeing a backref node
- btrfs_backref_free_node: this just is kfree() essentially.
- btrfs_backref_drop_node: this actually unlinks the node and cleans up
everything and then calls btrfs_backref_free_node().
We should mostly be using btrfs_backref_drop_node(), to make sure the
node is properly unlinked from the backref cache, and only use
btrfs_backref_free_node() when we know the node isn't actually linked to
the backref cache. We made a mistake here and thus got the KASAN splat.
Make this style of issue easier to find by adding some ASSERT()'s to
btrfs_backref_free_node() and adjusting our deletion stuff to properly
init the list so we can rely on list_empty() checks working properly.
Signed-off-by: Josef Bacik <jo...@toxicpanda.com>
---
fs/btrfs/backref.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h
index ff705cc564a9..17abde7f794c 100644
--- a/fs/btrfs/backref.h
+++ b/fs/btrfs/backref.h
@@ -296,6 +296,9 @@ static inline void btrfs_backref_free_node(struct
btrfs_backref_cache *cache,
struct btrfs_backref_node *node)
{
if (node) {
+ ASSERT(list_empty(&node->list));
+ ASSERT(list_empty(&node->lower));
+ ASSERT(node->eb == NULL);
cache->nr_nodes--;
btrfs_put_root(node->root);
kfree(node);
@@ -340,11 +343,11 @@ static inline void btrfs_backref_drop_node_buffer(
static inline void btrfs_backref_drop_node(struct btrfs_backref_cache *tree,
struct btrfs_backref_node *node)
{
- BUG_ON(!list_empty(&node->upper));
+ ASSERT(list_empty(&node->upper));
btrfs_backref_drop_node_buffer(node);
- list_del(&node->list);
- list_del(&node->lower);
+ list_del_init(&node->list);
+ list_del_init(&node->lower);
if (!RB_EMPTY_NODE(&node->rb_node))
rb_erase(&node->rb_node, &tree->rb_root);
btrfs_backref_free_node(tree, node);
--
2.26.2
