On Sat, Nov 11, 2023 at 01:06:01PM +0800, Edward Adam Davis wrote: > +++ b/fs/btrfs/disk-io.c > @@ -4931,7 +4931,8 @@ int btrfs_get_free_objectid(struct btrfs_root *root, u64 *objectid) > goto out; > } > > - *objectid = root->free_objectid++; > + while (find_qgroup_rb(root->fs_info, root->free_objectid++)); > + *objectid = root->free_objectid; This looks buggy to me. Let's say that free_objectid is currently 3. Before, it would assign 3 to *objectid, and increment free_objectid to 4. After (assuming the loop terminates on first iteration), it will increment free_objectid to 4, then assign 4 to *objectid. I think you meant to write: while (find_qgroup_rb(root->fs_info, root->free_objectid)) root->free_objectid++; *objectid = root->free_objectid++; And the lesson here is that more compact code is not necessarily more correct code. (I'm not making any judgement about whether this is the correct fix; I don't understand btrfs well enough to have an opinion. Just that this is not an equivalent transformation)
