On Fri, 2019-01-11 at 13:48 +0100, Peter Zijlstra wrote: > I spotted this new v6 in my inbox and have rebased to it.
Thanks! > On Wed, Jan 09, 2019 at 01:01:48PM -0800, Bart Van Assche wrote: > > > The changes compared to v5 are: > > - Modified zap_class() such that it doesn't try to free a list entry that > > is already being freed. > > I however have a question on this; this seems wrong. Once a list entry > is enqueued it should not be reachable anymore. If we can reach an entry > after call_rcu() happened, we've got a problem. Apparently I confused you - sorry that I was not more clear. What I meant is that I changed a single if test into a loop. The graph lock is held while that loop is being executed so the code below is serialized against the code called from inside the RCU callback: @@ -4574,8 +4563,9 @@ static void zap_class(struct pending_free *pf, struct lock _class *class) entry = list_entries + i; if (entry->class != class && entry->links_to != class) continue; - if (__test_and_set_bit(i, pf->list_entries_being_freed)) + if (list_entry_being_freed(i)) continue; + set_bit(i, pf->list_entries_being_freed); nr_list_entries--; list_del_rcu(&entry->entry); } Please let me know if you need more information. Bart.