• David Ahern's avatar
    lwtunnel: fix autoload of lwt modules · 9ed59592
    David Ahern authored
    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: 745041e2 ("lwtunnel: autoload of lwt modules")
    Signed-off-by: default avatarDavid Ahern <dsa@cumulusnetworks.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9ed59592
fib_frontend.c 31.2 KB