This can be reproduced by removing the is_exclusive tag from the audit tests after https://reviews.freebsd.org/D28451 and running them in parallel. root@freebsd-amd64:/usr/tests/sys/audit # kyua -v parallelism=16 test administrative:adjtime_failure -> passed [0.153s] administrative:adjtime_success -> passed [0.149s] administrative:auditctl_failure -> failed: /local/scratch/alr48/cheri/freebsd/tests/sys/audit/utils.c:300: 0 != audit_quick_start(): Failed to start fake auditd: File exists [0.148s] administrative:auditctl_success -> passed [0.145s] administrative:auditon_default_failure -> passed [0.057s] administrative:auditon_default_success -> failed: /local/scratch/alr48/cheri/freebsd/tests/sys/audit/utils.c:300: 0 != audit_quick_start(): Failed to start fake auditd: File exists [0.143s] panic: audit_syscall_enter: td->td_ar != NULL cpuid = 0 time = 1612265481 KDB: stack backtrace: db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe0093bb59d0 vpanic() at vpanic+0x188/frame 0xfffffe0093bb5a20 panic() at panic+0x43/frame 0xfffffe0093bb5a80 audit_syscall_enter() at audit_syscall_enter+0x1b7/frame 0xfffffe0093bb5ac0 amd64_syscall() at amd64_syscall+0x702/frame 0xfffffe0093bb5bf0 fast_syscall_common() at fast_syscall_common+0xf8/frame 0xfffffe0093bb5bf0 --- syscall (3, FreeBSD ELF64, sys_read), rip = 0x8003e556a, rsp = 0x7fffffffca48, rbp = 0x7fffffffca60 --- KDB: enter: panic [ thread pid 809 tid 100093 ] Stopped at kdb_enter+0x37: movq $0,0x10a084e(%rip)