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Date:      Sun, 05 May 2019 21:18:08 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 237758] Loading and subsequent unloading of the dcons kernel module causes panic
Message-ID:  <bug-237758-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D237758

            Bug ID: 237758
           Summary: Loading and subsequent unloading of the dcons kernel
                    module causes panic
           Product: Base System
           Version: 12.0-STABLE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: admin@support.od.ua

Created attachment 204230
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=3D204230&action=
=3Dedit
kldstat -v

I have FreeBSD system:
# uname -a
FreeBSD core.domain.com 12.0-STABLE FreeBSD 12.0-STABLE r347079 SUPPORT-12-=
0-1=20
amd64


root@core:~ # kldload dcons.ko
root@core:~ #
root@core:~ # kldunload dcons.ko

And the system crashes...


root@core:~ # /usr/libexec/kgdb /boot/kernel/kernel /var/crash/vmcore.2
GNU gdb 6.1.1 [FreeBSD]
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain condition=
s.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "amd64-marcel-freebsd"...

Unread portion of the kernel message buffer:
dcons: unload
panic: Terminal device freed without a free-handler
cpuid =3D 0
time =3D 1557100854
KDB: stack backtrace:
#0 0xffffffff80cc3707 at kdb_backtrace+0x67
#1 0xffffffff80c775dd at vpanic+0x19d
#2 0xffffffff80c77433 at panic+0x43
#3 0xffffffff80cf81a2 at ttydevsw_deffree+0x12
#4 0xffffffff80cfa15d at tty_dealloc+0xad
#5 0xffffffff80c14c5c at destroy_dev_tq+0xac
#6 0xffffffff80cd5de4 at taskqueue_run_locked+0x154
#7 0xffffffff80cd5bd1 at taskqueue_run+0x71
#8 0xffffffff80c3a654 at ithread_loop+0x1d4
#9 0xffffffff80c374c3 at fork_exit+0x83
#10 0xffffffff81248a8e at fork_trampoline+0xe
Uptime: 1m52s
Dumping 268 out of 979 MB:..6%..12%..24%..36%..42%..54%..66%..72%..84%..96%

Reading symbols from /boot/kernel/zfs.ko...Reading symbols from
/usr/lib/debug//boot/kernel/zfs.ko.debug...done.
done.
Loaded symbols for /boot/kernel/zfs.ko
Reading symbols from /boot/kernel/opensolaris.ko...Reading symbols from
/usr/lib/debug//boot/kernel/opensolaris.ko.debug...done.
done.
Loaded symbols for /boot/kernel/opensolaris.ko
Reading symbols from /boot/kernel/dcons.ko...Reading symbols from
/usr/lib/debug//boot/kernel/dcons.ko.debug...done.
done.
Loaded symbols for /boot/kernel/dcons.ko
#0  doadump () at src/sys/amd64/include/pcpu.h:230
230             __asm("movq %%gs:%P1,%0" : "=3Dr" (td) : "n"
(OFFSETOF_CURTHREAD));

(kgdb) bt
#0  doadump () at src/sys/amd64/include/pcpu.h:230
#1  0xffffffff80c771d8 in kern_reboot (howto=3D260) at
/usr/src/sys/kern/kern_shutdown.c:451
#2  0xffffffff80c77639 in vpanic (fmt=3D<value optimized out>, ap=3D<value
optimized out>)
    at /usr/src/sys/kern/kern_shutdown.c:877
#3  0xffffffff80c77433 in panic (fmt=3D<value optimized out>) at
/usr/src/sys/kern/kern_shutdown.c:804
#4  0xffffffff80cf81a2 in ttydevsw_deffree (softc=3D<value optimized out>) =
at
/usr/src/sys/kern/tty.c:1007
#5  0xffffffff80cfa15d in tty_dealloc (arg=3D0xfffff800254ea000) at
src/sys/sys/ttydevsw.h:198
#6  0xffffffff80c14c5c in destroy_dev_tq (ctx=3D<value optimized out>,
pending=3D<value optimized out>)
    at /usr/src/sys/kern/kern_conf.c:1438
#7  0xffffffff80cd5de4 in taskqueue_run_locked (queue=3D0xfffff8000305db00)
    at /usr/src/sys/kern/subr_taskqueue.c:467
#8  0xffffffff80cd5bd1 in taskqueue_run (queue=3D0xfffff8000305db00) at
/usr/src/sys/kern/subr_taskqueue.c:486
#9  0xffffffff80c3a654 in ithread_loop (arg=3D<value optimized out>) at
/usr/src/sys/kern/kern_intr.c:1129
#10 0xffffffff80c374c3 in fork_exit (callout=3D0xffffffff80c3a480 <ithread_=
loop>,
arg=3D0xfffff80003111540,
    frame=3D0xfffffe0000434ac0) at /usr/src/sys/kern/kern_fork.c:1060
#11 0xffffffff81248a8e in fork_trampoline () at
/usr/src/sys/amd64/amd64/exception.S:995
#12 0x0000000000000000 in ?? ()
Current language:  auto; currently minimal

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