Hello, On Wed, Nov 13, 2024 at 02:23:33PM +0100, Sebastian Andrzej Siewior wrote: ... > > That is the easy part. kernfs_path_from_node() is different as it > > requires the parent pointer. In order to distinguish the RCU from the > > non-RCU version I need kernfs_root for the flag and depending on it, the > > lock so the parent does not go away. > > > > Would it work to add the pointer to kernfs_root into kernfs_node? This > > would shrink kernfs_elem_dir by a pointer but the union would remain the > > same size due to kernfs_elem_attr so the struct would grow. > > The kernfs_node is released via RCU. That means if the RCU read section > starts before kernfs_root() then we should always get a stable pointer, > pointing to the same kernfs_root node since it is always the same one. > Even if the `parent' pointer is replaced. Wouldn't we need __rcu > annotation then for the `parent' pointer then? Yeah, I think this is the better direction. Just make both the parent and name RCU protected, drop the rename rwlock and use RCU deref for both ->parent and ->name so that the code path doesn't have to diverge. Thanks. -- tejun
