On Tue, Sep 08, 2020 at 09:37:10AM -0600, David Ahern wrote:
> On 9/8/20 3:10 AM, Ido Schimmel wrote:
> > From: Ido Schimmel <ido...@nvidia.com>
> >
> > When registering a new notifier to the nexthop notification chain,
> > replay all the existing nexthops to the new notifier so that it will
> > have a complete picture of the available nexthops.
> >
> > Signed-off-by: Ido Schimmel <ido...@nvidia.com>
> > ---
> > net/ipv4/nexthop.c | 54 ++++++++++++++++++++++++++++++++++++++++++++--
> > 1 file changed, 52 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> > index b40c343ca969..6505a0a28df2 100644
> > --- a/net/ipv4/nexthop.c
> > +++ b/net/ipv4/nexthop.c
> > @@ -156,6 +156,27 @@ static int call_nexthop_notifiers(struct net *net,
> > return notifier_to_errno(err);
> > }
> >
> > +static int call_nexthop_notifier(struct notifier_block *nb, struct net
> > *net,
> > + enum nexthop_event_type event_type,
> > + struct nexthop *nh,
> > + struct netlink_ext_ack *extack)
> > +{
> > + struct nh_notifier_info info = {
> > + .net = net,
> > + .extack = extack,
> > + };
> > + int err;
> > +
> > + err = nh_notifier_info_init(&info, nh);
> > + if (err)
> > + return err;
> > +
> > + err = nb->notifier_call(nb, event_type, &info);
> > + nh_notifier_info_fini(&info);
> > +
> > + return notifier_to_errno(err);
> > +}
> > +
> > static unsigned int nh_dev_hashfn(unsigned int val)
> > {
> > unsigned int mask = NH_DEV_HASHSIZE - 1;
> > @@ -2116,11 +2137,40 @@ static struct notifier_block nh_netdev_notifier = {
> > .notifier_call = nh_netdev_event,
> > };
> >
> > +static int nexthops_dump(struct net *net, struct notifier_block *nb,
> > + struct netlink_ext_ack *extack)
> > +{
> > + struct rb_root *root = &net->nexthop.rb_root;
> > + struct rb_node *node;
> > + int err = 0;
> > +
> > + for (node = rb_first(root); node; node = rb_next(node)) {
> > + struct nexthop *nh;
> > +
> > + nh = rb_entry(node, struct nexthop, rb_node);
> > + err = call_nexthop_notifier(nb, net, NEXTHOP_EVENT_REPLACE, nh,
> > + extack);
> > + if (err)
> > + break;
> > + }
> > +
> > + return err;
> > +}
> > +
> > int register_nexthop_notifier(struct net *net, struct notifier_block *nb,
> > struct netlink_ext_ack *extack)
> > {
> > - return blocking_notifier_chain_register(&net->nexthop.notifier_chain,
> > - nb);
> > + int err;
> > +
> > + rtnl_lock();
> > + err = nexthops_dump(net, nb, extack);
>
> can the unlock be moved here? register function below should not need it.
It can result in this unlikely race:
<t0> - rtnl_lock(); nexthops_dump(); rtnl_unlock()
<t1> - Nexthop is added / deleted
<t2> - blocking_notifier_chain_register()
It is possible to flip the order:
<t0> - blocking_notifier_chain_register()
<t1> - rtnl_lock(); nexthops_dump(); rtnl_unlock()
Worst case:
<t0> - blocking_notifier_chain_register()
<t1> - Nexthop is added / deleted
<t2> - rtnl_lock(); nexthops_dump(); rtnl_unlock()
Which is OK. If we get a delete notification for a nexthop we don't
know, we ignore it. If we get two replace notifications for the same
nexthop we just "update" it.
>
> > + if (err)
> > + goto unlock;
> > + err = blocking_notifier_chain_register(&net->nexthop.notifier_chain,
> > + nb);
> > +unlock:
> > + rtnl_unlock();
> > + return err;
> > }
> > EXPORT_SYMBOL(register_nexthop_notifier);
> >
> >
>
