lwtunnel: fix autoload of lwt modules

Trying to add an mpls encap route when the MPLS modules are not loaded
hangs. For example:

    CONFIG_MPLS=y
    CONFIG_NET_MPLS_GSO=m
    CONFIG_MPLS_ROUTING=m
    CONFIG_MPLS_IPTUNNEL=m

    $ ip route add 10.10.10.10/32 encap mpls 100 via inet 10.100.1.2

The ip command hangs:
root       880   826  0 21:25 pts/0    00:00:00 ip route add 10.10.10.10/32 encap mpls 100 via inet 10.100.1.2

    $ cat /proc/880/stack
    [<ffffffff81065a9b>] call_usermodehelper_exec+0xd6/0x134
    [<ffffffff81065efc>] __request_module+0x27b/0x30a
    [<ffffffff814542f6>] lwtunnel_build_state+0xe4/0x178
    [<ffffffff814aa1e4>] fib_create_info+0x47f/0xdd4
    [<ffffffff814ae451>] fib_table_insert+0x90/0x41f
    [<ffffffff814a8010>] inet_rtm_newroute+0x4b/0x52
    ...

modprobe is trying to load rtnl-lwt-MPLS:

root       881     5  0 21:25 ?        00:00:00 /sbin/modprobe -q -- rtnl-lwt-MPLS

and it hangs after loading mpls_router:

    $ cat /proc/881/stack
    [<ffffffff81441537>] rtnl_lock+0x12/0x14
    [<ffffffff8142ca2a>] register_netdevice_notifier+0x16/0x179
    [<ffffffffa0033025>] mpls_init+0x25/0x1000 [mpls_router]
    [<ffffffff81000471>] do_one_initcall+0x8e/0x13f
    [<ffffffff81119961>] do_init_module+0x5a/0x1e5
    [<ffffffff810bd070>] load_module+0x13bd/0x17d6
    ...

The problem is that lwtunnel_build_state is called with rtnl lock
held preventing mpls_init from registering.

Given the potential references held by the time lwtunnel_build_state it
can not drop the rtnl lock to the load module. So, extract the module
loading code from lwtunnel_build_state into a new function to validate
the encap type. The new function is called while converting the user
request into a fib_config which is well before any table, device or
fib entries are examined.

Fixes: 745041e2aaf1 ("lwtunnel: autoload of lwt modules")
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/net/lwtunnel.h b/include/net/lwtunnel.h
index d4c1c75b8862..0b585f1fd340 100644
--- a/include/net/lwtunnel.h
+++ b/include/net/lwtunnel.h
@@ -105,6 +105,8 @@ int lwtunnel_encap_add_ops(const struct lwtunnel_encap_ops *op,
 			   unsigned int num);
 int lwtunnel_encap_del_ops(const struct lwtunnel_encap_ops *op,
 			   unsigned int num);
+int lwtunnel_valid_encap_type(u16 encap_type);
+int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int len);
 int lwtunnel_build_state(struct net_device *dev, u16 encap_type,
 			 struct nlattr *encap,
 			 unsigned int family, const void *cfg,
@@ -168,6 +170,15 @@ static inline int lwtunnel_encap_del_ops(const struct lwtunnel_encap_ops *op,
 	return -EOPNOTSUPP;
 }
 
+static inline int lwtunnel_valid_encap_type(u16 encap_type)
+{
+	return -EOPNOTSUPP;
+}
+static inline int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int len)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int lwtunnel_build_state(struct net_device *dev, u16 encap_type,
 				       struct nlattr *encap,
 				       unsigned int family, const void *cfg,