On Sun, 28 Jan 2024 13:08:55 -0800 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Sun, 28 Jan 2024 at 12:53, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > Now, the RCU delay may be needed if the lookup of said structure > > happens under RCU, but no, saying "I use SRCU to make sure the > > lifetime is at least X" is just broken. > > Put another way, the only reason for any RCU should be that you don't > use locking at lookup, and the normal lookup routine should follow a > pattern something like this: > > rcu_read_lock(); > entry = find_entry(...); > if (entry && !atomic_inc_not_zero(&entry->refcount)) > entry = NULL; > rcu_read_unlock(); > > and the freeing should basically follow a pattern like > > if (atomic_dec_and_test(&entry->refcount)) > rcu_free(entry); Basically you are saying that when the ei is created, it should have a ref count of 1. If the lookup happens and does the atomic_inc_not_zero() it will only increment if the ref count is not 0 (which is basically equivalent to is_freed). And then we can have deletion of the object happen in both where the caller (kprobes) deletes the directory and in the final iput() reference (can I use iput and not the d_release()?), that it does the same as well. Where whatever sees the refcount of zero calls rcu_free? -- Steve
