Hello, On Fri, Feb 14, 2020 at 10:50:01AM +0800, Yufen Yu wrote: > > So, unregistering can leave ->dev along and re-registering can test > > whether it's NULL and if not put the existing one and put a new one > > there. Wouldn't that work? > > Do you mean set bdi->dev as 'NULL' in call_rcu() callback function > (i.e. bdi_release_device()) and test 'bdi->dev' in bdi_register_va()? > > I think that may do not work. > We cannot make sure the order of rcu callback function and re-registering. > Then bdi_release_device() may put the new allocated device by re-registering. No, I meant not freeing bdi->dev on deregistration and only doing so when it actually needs to - on re-registration or release. So, sth like the following. * Unregister: Unregister bdi->dev but don't free it. Leave the pointer alone. * Re-register: If bdi->dev is not null, initiate RCU-free and update bdi->dev to the new dev. * Release: If bdi->dev is not NULL, initiate RCU-free of it. Thanks. -- tejun
