Re: [PATCH v1 net-next 04/13] net: Introduce init2() for pernet_operations.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 26 Aug 2022 08:20:06 -0700
> On Thu, Aug 25, 2022 at 5:06 PM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
> >
> > This patch adds a new init function for pernet_operations, init2().
> 
> Why ?
> 
> This seems not really needed...
> 
> TCP ops->init can trivially reach the parent net_ns if needed,
> because the current process is the one doing the creation of a new net_ns.

Yes, it's true because IPv4 TCP/UDP are both unloadable.

At first, I was thinking of a general interface, but I'm fine
to drop this patch and access current->nsproxy->net_ns like
sysctl_devconf_inherit_init_net does.


> 
> >
> > We call each init2() during clone() or unshare() only, where we can
> > access the parent netns for a child netns creation.
> >
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > ---
> >  include/net/net_namespace.h |  3 +++
> >  net/core/net_namespace.c    | 18 +++++++++++-------
> >  2 files changed, 14 insertions(+), 7 deletions(-)
> >
> > diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
> > index 8c3587d5c308..3ca426649756 100644
> > --- a/include/net/net_namespace.h
> > +++ b/include/net/net_namespace.h
> > @@ -410,6 +410,8 @@ struct pernet_operations {
> >          * from register_pernet_subsys(), unregister_pernet_subsys()
> >          * register_pernet_device() and unregister_pernet_device().
> >          *
> > +        * init2() is called during clone() or unshare() only.
> > +        *
> >          * Exit methods using blocking RCU primitives, such as
> >          * synchronize_rcu(), should be implemented via exit_batch.
> >          * Then, destruction of a group of net requires single
> > @@ -422,6 +424,7 @@ struct pernet_operations {
> >          * the calls.
> >          */
> >         int (*init)(struct net *net);
> > +       int (*init2)(struct net *net, struct net *old_net);
> >         void (*pre_exit)(struct net *net);
> >         void (*exit)(struct net *net);
> >         void (*exit_batch)(struct list_head *net_exit_list);
> > diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> > index 6b9f19122ec1..b120ff97d9f5 100644
> > --- a/net/core/net_namespace.c
> > +++ b/net/core/net_namespace.c
> > @@ -116,7 +116,8 @@ static int net_assign_generic(struct net *net, unsigned int id, void *data)
> >         return 0;
> >  }
> >
> > -static int ops_init(const struct pernet_operations *ops, struct net *net)
> > +static int ops_init(const struct pernet_operations *ops,
> > +                   struct net *net, struct net *old_net)
> >  {
> >         int err = -ENOMEM;
> >         void *data = NULL;
> > @@ -133,6 +134,8 @@ static int ops_init(const struct pernet_operations *ops, struct net *net)
> >         err = 0;
> >         if (ops->init)
> >                 err = ops->init(net);
> > +       if (!err && ops->init2 && old_net)
> > +               err = ops->init2(net, old_net);
> 
> If an error comes here, while ops->init() was a success, we probably
> leave things in a bad state (memory leak ?)

Somehow I thought .exit() should handle the case, yes, it's really bad
design... at least I should have added .exit2().

I'll drop this in v2.

Thank you!


> 
> >         if (!err)
> >                 return 0;
> >
> > @@ -301,7 +304,8 @@ EXPORT_SYMBOL_GPL(get_net_ns_by_id);
> >  /*
> >   * setup_net runs the initializers for the network namespace object.
> >   */
> > -static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
> > +static __net_init int setup_net(struct net *net, struct net *old_net,
> > +                               struct user_namespace *user_ns)
> >  {
> >         /* Must be called with pernet_ops_rwsem held */
> >         const struct pernet_operations *ops, *saved_ops;
> > @@ -323,7 +327,7 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
> >         mutex_init(&net->ipv4.ra_mutex);
> >
> >         list_for_each_entry(ops, &pernet_list, list) {
> > -               error = ops_init(ops, net);
> > +               error = ops_init(ops, net, old_net);
> >                 if (error < 0)
> >                         goto out_undo;
> >         }
> > @@ -469,7 +473,7 @@ struct net *copy_net_ns(unsigned long flags,
> >         if (rv < 0)
> >                 goto put_userns;
> >
> > -       rv = setup_net(net, user_ns);
> > +       rv = setup_net(net, old_net, user_ns);
> >
> >         up_read(&pernet_ops_rwsem);
> >
> > @@ -1107,7 +1111,7 @@ void __init net_ns_init(void)
> >         init_net.key_domain = &init_net_key_domain;
> >  #endif
> >         down_write(&pernet_ops_rwsem);
> > -       if (setup_net(&init_net, &init_user_ns))
> > +       if (setup_net(&init_net, NULL, &init_user_ns))
> >                 panic("Could not setup the initial network namespace");
> >
> >         init_net_initialized = true;
> > @@ -1148,7 +1152,7 @@ static int __register_pernet_operations(struct list_head *list,
> >
> >                         memcg = mem_cgroup_or_root(get_mem_cgroup_from_obj(net));
> >                         old = set_active_memcg(memcg);
> > -                       error = ops_init(ops, net);
> > +                       error = ops_init(ops, net, NULL);
> >                         set_active_memcg(old);
> >                         mem_cgroup_put(memcg);
> >                         if (error)
> > @@ -1188,7 +1192,7 @@ static int __register_pernet_operations(struct list_head *list,
> >                 return 0;
> >         }
> >
> > -       return ops_init(ops, &init_net);
> > +       return ops_init(ops, &init_net, NULL);
> >  }
> >
> >  static void __unregister_pernet_operations(struct pernet_operations *ops)
> > --
> > 2.30.2
> >