kern/53788: vt switching panic

[dholland%eecs.harvard.edu@localhost]

>Number:         53788
>Category:       kern
>Synopsis:       vt switching panic
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 15 10:55:00 +0000 2018
>Originator:     David Holland
>Release:        NetBSD 8.99.27 (20181205)
>Organization:
>Environment:
System: NetBSD macaran 8.99.27 NetBSD 8.99.27 (MACARAN) #50: Wed Dec 5 19:34:11 EST 2018 dholland@macaran:/usr/src/sys/arch/amd64/compile/MACARAN amd64
Architecture: x86_64
Machine: amd64
>Description:

	Switching from console 4 (running X :0) to console 1 (which
	had formerly been running X :1, but the X server had
	apparently cored a couple hours earlier without me noticing)
	with ctrl-alt-F2 triggered this panic:

	panic: kernel diagnostic assertion "!cpu_softintr_p()" failed: file "../../../../kern/subr_kmem.c", line 389 

I got a crashdump; trace follows:

#2  0xffffffff8074db35 in kern_assert (
    fmt=fmt@entry=0xffffffff8089b1f8 "kernel %sassertion \"%s\" failed: file \"%s\", line %d ") at ../../../../../../lib/libkern/kern_assert.c:51
#3  0xffffffff8051cc52 in kmem_free (p=0xffff80ea92db17f0, size=216)
    at ../../../../kern/subr_kmem.c:389
#4  0xffffffff804129b2 in usl_sync_done (sd=<optimized out>)
    at ../../../../dev/wscons/wsdisplay_compat_usl.c:138
#5  0xffffffff80412a40 in usl_sync_check_sig (sd=0xffff80ea92db17f0, sig=30, 
    flags=2) at ../../../../dev/wscons/wsdisplay_compat_usl.c:156
#6  0xffffffff80412ba2 in usl_attachproc (cookie=0xffff80ea92db17f0, 
    waitok=<optimized out>, callback=<optimized out>, cbarg=<optimized out>)
    at ../../../../dev/wscons/wsdisplay_compat_usl.c:253
#7  0xffffffff80411eab in wsdisplay_switch2 (dv=0xffff80ec217f8c88, error=0, 
    waitok=0) at ../../../../dev/wscons/wsdisplay.c:1978
#8  0xffffffff80508ba6 in callout_softclock (v=<optimized out>)
    at ../../../../kern/kern_timeout.c:739
#9  0xffffffff804fcc0b in softint_execute (l=<optimized out>, s=2, 
    si=0xffff84808adb00c0) at ../../../../kern/kern_softint.c:592
#10 softint_dispatch (pinned=<optimized out>, s=2)
    at ../../../../kern/kern_softint.c:874
#11 0xffffffff8021d21f in Xsoftintr ()

>How-To-Repeat:
	Unclear. Haven't seen this before, but this kernel was new
	last week so there have been relatively few opportunities to
	trigger it. (But I often vt switch a lot and often run
	multiple X servers.)

>Fix:
	Dunno. Not obvious from the trace why it doesn't do this every
	time, but it clearly doesn't.