On Wed, Mar 23, 2016 at 3:59 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > On Wed, 2016-03-23 at 15:36 -0700, Tom Herbert wrote: >> This patches adds udp6_lib_lookup_skb_noref, udp4_lib_lookup_skb_noref >> and related support to allow a caller to lookup a UDP socket >> without automatically taking a reference. The lookup and caller >> use of the socket must be done under rcu_read_lock. >> >> This feature will be used in a fast receive encapsulation path and >> also when performing GRO through callout in the UDP socket. >> >> Signed-off-by: Tom Herbert <t...@herbertland.com> >> --- > > As already mentioned in the past, you can not do a UDP lookup without > taking a reference, because we use SLAB_DESTROY_BY_RCU rules which are > strict. > > Only taking a reference and re-doing the keys check can make sure the > lookup result makes sense (as we check multiple words and there is no > way it can be done atomically) > > This is explained in include/linux/slab.h and > Documentation/RCU/rculist_nulls.txt > > If you want that to happen, we need first to not use > SLAB_DESTROY_BY_RCU. > > Then, we do not need to take a reference at all, even for the regular > UDP stack unicast receive path. > Thanks Eric. Do you think it is reasonable to not use SLAB_DESTROY_BY_RCU for UDP since it probably has a much lower allocation rate than what we'd see in TCP?
Tom > >
