The can_rx_unregister() can be called from NAPI (soft IRQ) context, at least
by j1939 stack. This leads to potential dead lock with &net->can.rcvlists_lock
called from can_rx_register:
===============================================================================
 WARNING: inconsistent lock state
 4.19.0-20181029-1-g3e67f95ba0d3 #3 Not tainted
 --------------------------------
 inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
 testj1939/224 [HC0[0]:SC1[1]:HE1:SE0] takes:
 1ad0fda3 (&(&net->can.rcvlists_lock)->rlock){+.?.}, at: can_rx_unregister+0x4c/0x1ac
 {SOFTIRQ-ON-W} state was registered at:
   lock_acquire+0xd0/0x1f4
   _raw_spin_lock+0x30/0x40
   can_rx_register+0x5c/0x14c
   j1939_netdev_start+0xdc/0x1f8
   j1939_sk_bind+0x18c/0x1c8
   __sys_bind+0x70/0xb0
   sys_bind+0x10/0x14
   ret_fast_syscall+0x0/0x28
   0xbedc9b64
 irq event stamp: 2440
 hardirqs last  enabled at (2440): [<c01302c0>] __local_bh_enable_ip+0xac/0x184
 hardirqs last disabled at (2439): [<c0130274>] __local_bh_enable_ip+0x60/0x184
 softirqs last  enabled at (2412): [<c08b0bf4>] release_sock+0x84/0xa4
 softirqs last disabled at (2415): [<c013055c>] irq_exit+0x100/0x1b0

 other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(&(&net->can.rcvlists_lock)->rlock);
   <Interrupt>
     lock(&(&net->can.rcvlists_lock)->rlock);

  *** DEADLOCK ***

 2 locks held by testj1939/224:
  #0: 168eb13b (rcu_read_lock){....}, at: netif_receive_skb_internal+0x3c/0x350
  #1: 168eb13b (rcu_read_lock){....}, at: can_receive+0x88/0x1c0
===============================================================================

To avoid this situation, we should use spin_lock_bh() instead of spin_lock().
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>