On Fri, Oct 05, 2018 at 08:45:40PM -0700, Paul E. McKenney wrote: > > Shouldn't the synchronize_rcu() precede the loop doing the kfree() > calls? Or am I missing something subtle? No, that was a cut and paste error on my part. I was removing the rcu_read_unlock() before the kfree loop, and accidentally removed the synchronize_rcu(). Then when I put it back, I put it back in the right place. The longer version: I originally used rcu_read_lock() and rcu_read_unlock() around setting up to_free[] --- since whatisRCU.txt didn't talk about rcu_derefence_proctected(), just rcu_dereference() in Section 2: "What is RCU's Core API?" Then when I looked at the example in Section 3, I was surprised when I didn't see the rcu_read_[un]lock() on the updater side, and spent some time trying to figure out how to use rcu_dereference_protected(). Then when I did the transumation from rcu_read_lock/rcu_dereference_protected/rcu_read_unlock to rcu_dereference_protected, I bobbled the location of synchronize_rcu(). - Ted P.S. Pedagogically, it might make sense to show an example that only uses the RCU core API --- I assume using rcu_read_[un]lock() and rcu_dereference() does work; it's just non-optimal, right? --- and then introduce the use of rcu_dereference_protected() afterwards.
