On Fri, Dec 8, 2017 at 1:40 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > On Fri, 2017-12-08 at 13:28 +0800, Tonghao Zhang wrote: >> On Fri, Dec 8, 2017 at 1:20 AM, Eric Dumazet <eric.duma...@gmail.com> >> wrote: >> > On Thu, 2017-12-07 at 08:45 -0800, Tonghao Zhang wrote: >> > > In some case, we want to know how many sockets are in use in >> > > different _net_ namespaces. It's a key resource metric. >> > > >> > >> > ... >> > >> > > +static void sock_inuse_add(struct net *net, int val) >> > > +{ >> > > + if (net->core.prot_inuse) >> > > + this_cpu_add(*net->core.sock_inuse, val); >> > > +} >> > >> > This is very confusing. >> > >> > Why testing net->core.prot_inuse for NULL is needed at all ? >> > >> > Why not testing net->core.sock_inuse instead ? >> > >> >> Hi Eric and Cong, oh it's a typo. it's net->core.sock_inuse there. >> Why >> we should check the net->core.sock_inuse >> Now show you the code: >> >> cleanup_net will call all of the network namespace exit methods, >> rcu_barrier, and then remove the _net_ namespace. >> >> cleanup_net: >> list_for_each_entry_reverse(ops, &pernet_list, list) >> ops_exit_list(ops, &net_exit_list); >> >> rcu_barrier(); /* for netlink sock, the ‘deferred_put_nlk_sk’ >> will >> be called. But sock_inuse has been released. */ > > > Thats would be a bug. > > Please find another way, but we want ultimately to check that before > net->core.sock_inuse is freed, folding the inuse count on all cpus is > 0, to make sure we do not have a bug somewhere.
Yes, I am aware of this issue even we will destroy the network namespace. By the way, we can counter the socket-inuse in sock_alloc or sock_release. In this way, we have to hold the network namespace again(via get_net()) while sock may hold it. what do you think of this idea? > We should not have to test if net->core.sock_inuse is NULL or not from > sock_inuse_add(). Pointer must be there all the time. > > The freeing should only happen once we are sure sock_inuse_add() can > not be called anymore. > >> >> >> /* Finally it is safe to free my network namespace structure */ >> list_for_each_entry_safe(net, tmp, &net_exit_list, exit_list) {} >> >> >> >> Release the netlink sock created in kernel(not hold the _net_ >> namespace): >> >> netlink_release >> call_rcu(&nlk->rcu, deferred_put_nlk_sk); >> >> deferred_put_nlk_sk >> sk_free(sk); >> >> >> I may add a comment for sock_inuse_add in v6. > >