o_raw_spin_lock+0x131/0x140
[  296.821648]  [<ffffffff8169188e>] _raw_spin_lock+0x1e/0x20
[  296.821786]  [<ffffffffa00cc0fd>] __pktgen_NN_threads+0x4d/0x140 [pktgen]
[  296.821928]  [<ffffffffa00ccf8d>] pktgen_device_event+0x10d/0x1e0 [pktgen]
[  296.822073]  [<ffffffff8154ed4f>] unregister_netdevice_notifier+0x7f/0x100
[  296.822216]  [<ffffffffa00d2a0b>] pg_cleanup+0x48/0x73 [pktgen]
[  296.822357]  [<ffffffff8109528e>] sys_delete_module+0x17e/0x2a0
[  296.822502]  [<ffffffff81699652>] system_call_fastpath+0x16/0x1b

Hold the pktgen_thread_lock while splicing pktgen_threads, and test
pktgen_exiting in pktgen_device_event() to make unload faster.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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