panic: udp6_output: non-excl udbinfo lock, excl inp lock: pcbinfo ADDR 0x1 inp ADDR 0x2

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: e589cda9 amd64 pmap: block on turnstile for lock-less DI.
git tree: freebsd
console output: https://syzkaller.appspot.com/x/log.txt?x=162bb036a00000
dashboard link: https://syzkaller.appspot.com/bug?extid=c5ffbc8f14294c7b0e54

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c5ffbc...@syzkaller.appspotmail.com

panic: udp6_output: non-excl udbinfo lock, excl inp lock: pcbinfo
0xfffffe000026f9c8 0x1 inp 0xfffff80003db97a0 0x2
cpuid = 0
time = 135
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x47/frame
0xfffffe0020f0d4b0
vpanic() at vpanic+0x1e0/frame 0xfffffe0020f0d510
panic() at panic+0x43/frame 0xfffffe0020f0d570
udp6_send() at udp6_send+0x1175/frame 0xfffffe0020f0d730
sosend_dgram() at sosend_dgram+0x550/frame 0xfffffe0020f0d7a0
sosend() at sosend+0xc6/frame 0xfffffe0020f0d810
kern_sendit() at kern_sendit+0x35e/frame 0xfffffe0020f0d8c0
sendit() at sendit+0x225/frame 0xfffffe0020f0d920
sys_sendmsg() at sys_sendmsg+0x8b/frame 0xfffffe0020f0d980
amd64_syscall() at amd64_syscall+0x436/frame 0xfffffe0020f0dab0
fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe0020f0dab0
--- syscall (198, FreeBSD ELF64, nosys), rip = 0x4131fa, rsp =
0x7fffdffdcf38, rbp = 0x3 ---
KDB: enter: panic
[ thread pid 8639 tid 100869 ]
Stopped at kdb_enter+0x6a: movq $0,kdb_why


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