On Fri, Feb 16, 2018 at 04:09:32PM +0100, John Ogness wrote: > > inode = dentry->d_inode; > rcu_read_lock(); <- Protects d_inode from being freed, > i.e. dentry->d_inode is a valid pointer > even after dentry->d_lock is dropped > unlock(dentry->d_lock); > lock(inode->i_lock); > lock(dentry->d_lock); > rcu_read_unlock();
So that is entirely tricky, typically we have to have a lookup _after_ rcu_read_lock(). Here, we rely on not being able to call dentry_free() while we hold d_lock, which ensure dentry must be valid in the freshly started rcu-section. And I suppose that same ensures dentry->d_ionde stays alive. But this needs a comment at least.
