kern/54397: Panic when loading a DTrace module whilst DTrace is running

[venture37%geeklan.co.uk@localhost]

>Number:         54397
>Category:       kern
>Synopsis:       Panic when loading a DTrace module whilst DTrace is running
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 22 17:20:00 +0000 2019
>Originator:     Sevan Janiyan
>Release:        HEAD
>Organization:
>Environment:
NetBSD 8.99.51 (GENERIC) #0: Thu Jul 18 20:10:46 UTC 2019  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
>Description:
When running a DTrace script you can trigger a system panic by loading a new DTrace kernel module despite not being in use. e.g running a script which makes use of the syscall provider via the dtrace_syscall module & loading the dtrace_fbt module.

uvm_fault(0xffffdf05ff1b8470, 0x0, 1) -> e
fatal page fault in supervisor mode
trap type 6 code 0 rip 0xffffffff82575298 cs 0x8 rflags 0x10246 cr2 0x8 ilevel 0 rsp 0xffffb980b0b63ca0
curlwp 0xffffdf05f4f176e0 pid 1004.1 lowest kstack 0xffffb980b0b602c0

stopped in pid 1004.1 (modload) at solaris:taskq_dispatch+0x25: testb $
0x4,8(%r12)

taskq_dispatch() at solaris:taskq_dispatch+0x25
dtrace_module_loaded() at dtrace:dtrace_module_loaded+0x9b
module_do_load() at netbsd:module_db_load+0xb0d
module_load() at netbsd:module_load+0xa4
handle_modctl_load() at netbsd:handle_modctl_load+0x143
sys_modctl() at netbsd:sys_modctl+0xdd
syscall() at netbsd:syscall_modctl+0x181
--- syscall (number 246) ---
7adc8484311a:
>How-To-Repeat:
Start without any dtrace modules loaded
Run execsnoop
Whilst execsnoop is running, modload dtrace_fbt or any other dtrace module currently not loaded.
>Fix: