Building the linux-wireless-testing tree described in https://wireless.wiki.kernel.org/en/developers/documentation/git-guide I have multiple MediaTek 7612 USB cards I’d like to get working. There’s exciting work going on in wireless to bring the MediaTek wifi into the mainline kernel.
I built the kernel on a Shuttle, loaded my new kernel. Plugged in the Alfa AWUS036ACM dongle, loaded up wpa_supplicant and my scripts. Desktop was unresponsive: hard lock up.
Power cycle. I’m on Fedora 28 which is systemd which uses journald. The journalctl -b -1 didn’t show any kernel panic.
Debugging a hard lock up of a kernel module seems easier than a kernel boot. The netconsole module https://www.kernel.org/doc/Documentation/networking/netconsole.txt will let me see the kernel log messages leading up to the lock-up.
I also need to investigate the watchdogs https://www.kernel.org/doc/Documentation/lockup-watchdogs.txt
% sudo modprobe netconsole @/enp3s0,email@example.com/
[69677.819810] netconsole: unknown parameter '@/enp3s0,5566@172' ignored [69677.819903] console [netcon0] enabled [69677.819904] netconsole: network logging started
OK, what did I screw up. Is there a way I can tickle the kernel into logging a message to test my config? Not from userspace, but Google search found the following useful post. (Oh, StackOverflow (and related) is there nothing you can’t do?)
Load/unload the module. Still not seeing any messages. Oh, right. I always forget this step. https://elinux.org/Debugging_by_printing#Netconsole_resources
echo 8 > /proc/sys/kernel/debug
Skipping over the “unknown parameter” problem for now and just setting the parameters manually. Here is what I have:
...trillian:coconut% cd /sys/kernel/config/netconsole/ ...trillian:netconsole% ls arthurdent/ ...trillian:netconsole% cd arthurdent/ ...trillian:arthurdent% ls dev_name enabled extended local_ip local_mac local_port remote_ip remote_mac remote_port ...trillian:arthurdent% cat remote_mac 70:88:6b:81:ac:64 ...trillian:arthurdent% cat remote_ip 172.16.17.181 ...trillian:arthurdent% cat remote_port 5566 ...trillian:arthurdent% cat local_ip 172.16.17.92 ...trillian:arthurdent% cat local_port 6665 ...trillian:arthurdent% cat dev_name enp0s31f6
So now run netcat on arthurdent, my other machine.
nc -l -u 5566
Can test my netcat from trillian by sending a udp packet:
ls | nc -u 172.16.17.181 5566
And now time to turn the crank and watch the chaos unfold. Start up my wpa_supplicant and wpa_cli script and boom crash.
[ 546.841947] wlp0s20f0u1u2: authenticate with c4:b9:cd:dc:48:40 [ 547.140202] wlp0s20f0u1u2: send auth to c4:b9:cd:dc:48:40 (try 1/3) [ 547.140226] BUG: unable to handle kernel NULL pointer dereference at 0000000000000011 [ 547.140228] PGD 800000083e025067 P4D 800000083e025067 PUD 83e072067 PMD 0 [ 547.140233] Oops: 0000 [#1] SMP PTI [ 547.140236] CPU: 2 PID: 2503 Comm: wpa_supplicant Not tainted 4.19.0-rc2-wt #1 [ 547.140238] Hardware name: Shuttle Inc. SZ170/FZ170, BIOS 2.09 08/01/2017 [ 547.140258] RIP: 0010:ieee80211_wake_txqs+0x1e3/0x3d0 [mac80211] [ 547.140261] Code: 4c 89 fe 4c 89 ef 48 8b 92 b0 02 00 00 e8 45 d6 2e f4 48 8b 3c 24 e8 0c bc 00 f4 48 83 c5 08 48 3b 6c 2 4 08 74 a0 4c 8b 7d 00 <41> 0f b6 57 11 3b 54 24 18 75 e6 4d 8d a7 28 ff ff ff f0 49 0f ba [ 547.140263] RSP: 0018:ffff95038ea83ed0 EFLAGS: 00010293 [ 547.140265] RAX: ffff95038419e978 RBX: ffff95038419e000 RCX: ffff950384b18760 [ 547.140267] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff950384b18828 [ 547.140269] RBP: ffff95038419e970 R08: 00039e862fcdb16e R09: ffff95038a9b4230 [ 547.140271] R10: 0000000000000420 R11: ffffb8efc46c78d0 R12: ffff9503798251d0 [ 547.140273] R13: ffff950384b18760 R14: 0000000000000000 R15: 0000000000000000 [ 547.140275] FS: 00007f42ed60cdc0(0000) GS:ffff95038ea80000(0000) knlGS:0000000000000000 [ 547.140277] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 547.140279] CR2: 0000000000000011 CR3: 0000000835b30001 CR4: 00000000003606e0 [ 547.140281] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 547.140283] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 547.140284] Call Trace:
(Crash truncated here.) Posted to the linux-wireless mailing list and am now getting some help.