kern/40734: crash in comintr()

[Christoph_Egger%gmx.de@localhost]

>Number:         40734
>Category:       kern
>Synopsis:       crash in comintr()
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 24 12:30:00 +0000 2009
>Originator:     Christoph Egger
>Release:        5.99.7
>Organization:
>Environment:
NetBSD/amd64 5.99.7
>Description:

Run NetBSD/amd64 with serial console.

<dmesg snippet>
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com0: console
</dmesg snippet>

Very rarely a sudden crash happens in sys/dev/ic/com.c:comintr()
in this line:

iir = CSR_READ_1(regsp, COM_REG_IIR);

regsp is a NULL pointer when the crash happens.

fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip 0xffffffff802380d5 cs 8 rflags 202 cr2 ffff80004e810000 
cpl 8 rsp ffff80004ba75ad8
db> bt
breakpoint+0x5
comintr+0x53a
Xintr_ioapic_edge10+0xef
--- interrupt ---
x86_stihlt+0x6
idle_loop+0x198
db> machine cpu 1
Using cpu 1
db> bt
acpitimer_read_safe+0x18
binuptime+0x3b
mi_switch+0x4a
idle_loop+0xda


>How-To-Repeat:

>Fix: