usbus_cdc_ecm: failed assertion when host reboots

[benpicco]

Description

After a reboot I found my RIOT USB device unresponsive. It turns out it failed an assertion when the host rebooted.

Steps to reproduce the issue

Run the tests/sys/usbus_cdc_ecm application and reboot the host system.
In this case I had the Device USB port of the saml21-xpro connected to a Raspberry Pi and the Debug USB port connected to my laptop.

Expected results

Normal operation continues

Actual results

2023-05-24 18:12:34,954 - INFO # > sys/usb/usbus/usbus.c:285 => 
2023-05-24 18:12:34,956 - INFO # Context before hardfault:
2023-05-24 18:12:34,958 - INFO #    r0: 0x0000001d
2023-05-24 18:12:34,959 - INFO #    r1: 0x00000020
2023-05-24 18:12:34,961 - INFO #    r2: 0x00000019
2023-05-24 18:12:34,963 - INFO #    r3: 0x00000173
2023-05-24 18:12:34,964 - INFO #   r12: 0x00000019
2023-05-24 18:12:34,966 - INFO #    lr: 0x0000e867
2023-05-24 18:12:34,968 - INFO #    pc: 0x00000172
2023-05-24 18:12:34,969 - INFO #   psr: 0x21000000
2023-05-24 18:12:34,969 - INFO # 
2023-05-24 18:12:34,970 - INFO # Misc
2023-05-24 18:12:34,972 - INFO # EXC_RET: 0xfffffffd
2023-05-24 18:12:34,974 - INFO # Active thread: 3 "usbus"
2023-05-24 18:12:34,978 - INFO # Attempting to reconstruct state for debugging...
2023-05-24 18:12:34,979 - INFO # In GDB:
2023-05-24 18:12:34,980 - INFO #   set $pc=0x172
2023-05-24 18:12:34,981 - INFO #   frame 0
2023-05-24 18:12:34,982 - INFO #   bt
2023-05-24 18:12:34,984 - INFO # *** RIOT kernel panic:
2023-05-24 18:12:34,985 - INFO # HARD FAULT HANDLER
2023-05-24 18:12:34,985 - INFO # 
2023-05-24 18:12:34,994 - INFO # 	pid | name                 | state    Q | pri | stack  ( used) ( free) | base addr  | current     
2023-05-24 18:12:35,003 - INFO # 	  - | isr_stack            | -        - |   - |    512 (  488) (   24) | 0x20000000 | 0x200006a8
2023-05-24 18:12:35,012 - INFO # 	  1 | main                 | bl mutex _ |   7 |   1536 (  676) (  860) | 0x2000100c | 0x20001424 
2023-05-24 18:12:35,021 - INFO # 	  2 | ipv6                 | bl rx    _ |   4 |   1024 (  544) (  480) | 0x200016e8 | 0x200019cc 
2023-05-24 18:12:35,030 - INFO # 	  3 | usbus                | running  Q |   1 |   1024 (  892) (  132) | 0x200004dc | 0x2000075c 
2023-05-24 18:12:35,039 - INFO # 	  4 | cdcecm               | bl anyfl _ |   2 |    896 (  300) (  596) | 0x20002030 | 0x200022f4 
2023-05-24 18:12:35,046 - INFO # 	    | SUM                  |            |     |   4992 ( 2900) ( 2092)
2023-05-24 18:12:35,046 - INFO # 
2023-05-24 18:12:35,047 - INFO # *** halted.

-> https://github.com/RIOT-OS/RIOT/blob/master/sys/usb/usbus/usbus.c#L285

Versions

RIOT master