On Fri, Oct 28, 2022 at 11:29:00AM +0200, Niklas Schnelle wrote: > > rcu_head = kzalloc(rcu_head, GFP_NOWAIT, GFP_NOWARN) > > if (!rcu_head) > > synchronize_rcu() > > else > > call_rcu(rcu_head) > > > > And then call kmem_cache_free() from the rcu callback > > Hmm, maybe a stupid question but why can't I just put the rcu_head in > struct s390_domain and then do a call_rcu() on that with a callback > that does: > > dma_cleanup_tables(s390_domain->dma_table); > kfree(s390_domain); > > I.e. the rest of the current s390_domain_free(). > Then I don't have to worry about failing to allocate the rcu_head and > it's simple enough. Basically just do the actual freeing of the > s390_domain via call_rcu(). Oh, if you never reallocate the dma_table then yes that is a good idea > Or do you mean to use a kref that is taken by RCU readers together with > rcu_read_lock() and dropped at rcu_read_unlock() such that during the > RCU read critical sections the refcount can't fall below 1 and the > domain is actually freed once we have a) put the initial reference > during s390_domain_free() and b) put all temporary references on > exiting the RCU read critical sections? Yes, this is a common pattern. Usually you want to optimize away the global lock that protects, say, a linked list and then accept a local lock/refcount inside the object Jason
