[Merge] popcorn_migrate crashes when duplicate ips in the nodes file

[AHatnarf]

When /etc/popcorn/nodes has duplicate ips, i.e:

192.168.122.2
127.0.0.1
192.168.122.2
127.0.0.1

When inserting the module:

popcorn@x86:~$ sudo insmod msg_socket.ko
[  T723] Loading Popcorn messaging layer over TCP/IP...
[  T723] popcorn: Loading node configuration...
[  T723] popcorn:   0: 192.168.122.2
[  T723] popcorn: * 1: 127.0.0.1
[  T723] popcorn:   2: 192.168.122.2
[  T723] popcorn: * 3: 127.0.0.1
[  T723] Replace hot transport at your own risk.
[  T723] Ready to accept incoming connections
[  T723] Connecting to 0 at 192.168.122.2
[  T725] SEND handler for 0 is ready
[  T723] Connecting to 1 at 127.0.0.1
[  T726] RECV handler for 0 is ready
[  T727] SEND handler for 1 is ready
[  T723] Connecting to 2 at 192.168.122.2
[  T728] RECV handler for 1 is ready
[  T729] SEND handler for 2 is ready
[  T730] RECV handler for 2 is ready
[  T723] popcorn: Ready on TCP/IP
popcorn@x86:~$ sudo insmod msg_socket.ko 

Migration fails when running the basic test, with the following trace:

popcorn@x86:~/src$ ./basic
[  T745] ####### MIGRATE [745] to 1
[  T745] ------------[ cut here ]------------
[  T745] kernel BUG at ./include/popcorn/regset.h:94!
[  T745] invalid opcode: 0000 [#2] SMP NOPTI
[  T745] CPU: 0 PID: 745 Comm: basic Tainted: G      D W  O      5.2.0-rc4-popcorn+ #44
[  T745] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[  T745] RIP: 0010:process_server_do_migration+0x501/0x7f0
[  T745] Code: 00 e9 9b fd ff ff 0f 0b e9 94 fd ff ff 48 89 ef e8 d4 11 00 00 e9 87 fd ff ff 85 c0 41 89 c5 0f 84 2e fd ff ff e9 f8 fc ff ff <0f> 0b 0f 0b 8b b3 c8 03 00 00 8b 4d 0a 89 c2 48 c7 c7 c0 2e b7 81
[  T745] RSP: 0018:ffffc90000257e50 EFLAGS: 00000282
[  T745] RAX: 00000000ffffffff RBX: ffff888058471000 RCX: ffff88805847127e
[  T745] RDX: 0000000000000002 RSI: 0000000000000001 RDI: 0000000000000001
[  T745] RBP: ffff88805a1432c0 R08: 0000000000000000 R09: 0000000000000000
[  T745] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88805a558300
Travel for 118 ms
[  T745] R13: 0000000000000001 R14: 00007fffffffe900 R15: 0000000000000000
[  T745] FS:  00000000004ab880(0000) GS:ffff88805ba00000(0000) knlGS:0000000000000000
[  T745] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  T745] CR2: 00000000004ada38 CR3: 000000005861e000 CR4: 00000000000006f0
[  T745] Call Trace:
[  T745]  __se_sys_popcorn_migrate+0x75/0x130
[  T745]  __x64_sys_popcorn_migrate+0x16/0x20
[  T745]  do_syscall_64+0x69/0x440
[  T745]  ? trace_hardirqs_off_thunk+0x1a/0x1c
[  T745]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  T745] RIP: 0033:0x401e98
[  T745] Code: 44 0f 7f bd 40 ff ff ff 48 c7 85 80 fd ff ff 98 1e 40 00 48 8d 95 80 fd ff ff 8b bd 6c fd ff ff 48 89 d6 b8 b2 01 00 00 0f 05 <0f> ae f0 48 8b ad b8 fd ff ff 48 8b 9d a0 fd ff ff 4c 8b a5 e8 fd
[  T745] RSP: 002b:00007fffffffe8d0 EFLAGS: 00000246 ORIG_RAX: 00000000000001b2
[  T745] RAX: ffffffffffffffda RBX: 0000000000000076 RCX: 0000000000401e98
[  T745] RDX: 00007fffffffe900 RSI: 00007fffffffe900 RDI: 0000000000000001
[  T745] RBP: 00007fffffffeb80 R08: 0000000000000000 R09: 0000000000000012
[  T745] R10: 00007fffffffea65 R11: 0000000000000246 R12: 0000000000402f60
[  T745] R13: 0000000000000000 R14: 00000000004a7018 R15: 0000000000000000
[  T745] Modules linked in: msg_socket(O) [last unloaded: msg_socket]
[  T745] ---[ end trace f952d52dca275b48 ]---
[  T745] RIP: 0010:sock_recvmsg+0xf/0x30
[  T745] Code: c8 ff e9 24 ff ff ff e8 af 75 c3 ff 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 48 8b 47 28 4c 8b 46 20 89 d1 <48> 8b 80 80 00 00 00 4c 89 c2 48 3d 70 d4 4d 81 75 05 e9 fa 33 0b
[  T745] RSP: 0018:ffffc90000147e20 EFLAGS: 00000282
[  T745] RAX: 0000000000000000 RBX: ffff88805a39c4c0 RCX: 0000000000000100
[  T745] RDX: 0000000000000100 RSI: ffffc90000147e68 RDI: ffff8880579038c0
[  T745] RBP: ffffc90000147e68 R08: 0000000000000072 R09: 0000000000000100
[  T745] R10: ffff8880579038c0 R11: 0000000000000000 R12: ffffffffffffffff
[  T745] R13: ffff8880579038c0 R14: 0000000000000100 R15: ffffffffa00002c0
[  T745] FS:  00000000004ab880(0000) GS:ffff88805ba00000(0000) knlGS:0000000000000000
[  T745] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  T745] CR2: 00000000004ada38 CR3: 000000005861e000 CR4: 00000000000006f0
[  T745] EXITED [745] local / 0xb

We likely would need to make sure entries are deduplicated in the msg_layer.