Re: [btrfs?] KASAN: slab-use-after-free Read in add_delayed_ref

[Edward Adam Davis]

using delayed_refs->lock to sync btrfs_work_helper and add_delayed_ref

#syz test

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index 13c2e00d1270..cb57e65c9872 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -1058,7 +1058,6 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans,
 	head_ref = new_head_ref;
 
 	merged = insert_delayed_ref(trans, head_ref, node);
-	spin_unlock(&delayed_refs->lock);
 
 	/*
 	 * Need to update the delayed_refs_rsv with any changes we may have
@@ -1073,8 +1072,12 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans,
 	if (merged)
 		kmem_cache_free(btrfs_delayed_ref_node_cachep, node);
 
-	if (qrecord_inserted)
-		return btrfs_qgroup_trace_extent_post(trans, record, head_ref->bytenr);
+	if (qrecord_inserted) {
+		ret = btrfs_qgroup_trace_extent_post(trans, record, head_ref->bytenr);
+		spin_unlock(&delayed_refs->lock);
+		return ret;
+	}
+	spin_unlock(&delayed_refs->lock);
 	return 0;
 
 free_record: