kern/54802: gdb -p kills the kernel

[martin%NetBSD.org@localhost]

>Number:         54802
>Category:       kern
>Synopsis:       gdb -p kills the kernel
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Dec 27 11:00:00 +0000 2019
>Originator:     Martin Husemann
>Release:        NetBSD 9.99.30
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD seven-days-to-the-wolves.aprisoft.de 9.99.30 NetBSD 9.99.30 (GENERIC) #326: Fri Dec 27 08:14:06 CET 2019 martin%seven-days-to-the-wolves.aprisoft.de@localhost:/work/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:

Trying to debug a qemu hang (PR 54789) I attached gdb to the (only) qemu 
process running via gdb -p $pid.

This made the kernel crash imediately - but unfortunately the panic is not
100% reproducable.

Unfortunately no crash dump, ddb locked up after I tried to continue.

panic message (from memory): one of the two  KASSERT(l->l_stat != LSZOMB);
in kern_lwp.c failed (lwp_addref or lwp_delref), backtrace through various
ptrace_* functions.

>How-To-Repeat:

Download a recentish sparc64 iso and then:

 qemu-system-sparc64 -prom-env 'auto-boot?=false' -m 128 \
        -drive file=wd1.img,if=ide,index=0,media=disk,snapshot=off,format=raw \
        -drive file=wd0.img,if=ide,index=1,media=disk,snapshot=off,format=raw \
        -cdrom $ISO -nographic
 boot cdrom:f

In another window, do:

  gdb -p $( pgrep qemu )

and be unlucky.


>Fix:
n/a