On Sun, Jan 12, 2014 at 12:21:14PM -0800, Eric Dumazet wrote: > On Sun, 2014-01-12 at 21:50 +0400, Andrey Vagin wrote: > > Lets look at destroy_conntrack: > > > > hlist_nulls_del_rcu(&ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode); > > ... > > nf_conntrack_free(ct) > > kmem_cache_free(net->ct.nf_conntrack_cachep, ct); > > > > net->ct.nf_conntrack_cachep is created with SLAB_DESTROY_BY_RCU. > > > > The hash is protected by rcu, so readers look up conntracks without > > locks. > > A conntrack is removed from the hash, but in this moment a few readers > > still can use the conntrack. Then this conntrack is released and another > > thread creates conntrack with the same address and the equal tuple. > > After this a reader starts to validate the conntrack: > > * It's not dying, because a new conntrack was created > > * nf_ct_tuple_equal() returns true. > ... > > > > v2: move nf_ct_is_confirmed into the unlikely() annotation > > v3: Eric suggested to fix refcnt, so that it becomes zero before adding > > in a hash, but we can't find a way how to do that. Another way is to > > interpret the confirm bit as part of a search key and check it in > > ____nf_conntrack_find() too. > > > > Cc: Eric Dumazet <eric.duma...@gmail.com> > > Cc: Florian Westphal <f...@strlen.de> > > Cc: Pablo Neira Ayuso <pa...@netfilter.org> > > Cc: Patrick McHardy <ka...@trash.net> > > Cc: Jozsef Kadlecsik <kad...@blackhole.kfki.hu> > > Cc: "David S. Miller" <da...@davemloft.net> > > Cc: Cyrill Gorcunov <gorcu...@openvz.org> > > Signed-off-by: Andrey Vagin <ava...@openvz.org> > > --- > > Acked-by: Eric Dumazet <eduma...@google.com>
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