• Dan Streetman's avatar
    net: tcp: close sock if net namespace is exiting · 4ee806d5
    Dan Streetman authored
    When a tcp socket is closed, if it detects that its net namespace is
    exiting, close immediately and do not wait for FIN sequence.
    
    For normal sockets, a reference is taken to their net namespace, so it will
    never exit while the socket is open.  However, kernel sockets do not take a
    reference to their net namespace, so it may begin exiting while the kernel
    socket is still open.  In this case if the kernel socket is a tcp socket,
    it will stay open trying to complete its close sequence.  The sock's dst(s)
    hold a reference to their interface, which are all transferred to the
    namespace's loopback interface when the real interfaces are taken down.
    When the namespace tries to take down its loopback interface, it hangs
    waiting for all references to the loopback interface to release, which
    results in messages like:
    
    unregister_netdevice: waiting for lo to become free. Usage count = 1
    
    These messages continue until the socket finally times out and closes.
    Since the net namespace cleanup holds the net_mutex while calling its
    registered pernet callbacks, any new net namespace initialization is
    blocked until the current net namespace finishes exiting.
    
    After this change, the tcp socket notices the exiting net namespace, and
    closes immediately, releasing its dst(s) and their reference to the
    loopback interface, which lets the net namespace continue exiting.
    
    Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1711407
    Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=97811
    
    
    Signed-off-by: default avatarDan Streetman <ddstreet@canonical.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    4ee806d5