kern/43290: kern crash on socket read/write amd64 -current

[bch%methodlogic.net@localhost]

>Number:         43290
>Category:       kern
>Synopsis:       crash system networking on lo0
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 11 19:55:00 +0000 2010
>Originator:     bch%methodlogic.net@localhost
>Release:        NetBSD 5.99.29
>Organization:
        Method Logic Digital
        http://methodlogic.net
>Environment:
System: NetBSD kamloops 5.99.29 NetBSD 5.99.29 (kamloops) #30: Mon May 10 
22:55:08 PDT 2010 root@kamloops:/usr/obj/sys/arch/amd64/compile/kamloops amd64
Architecture: x86_64
Machine: amd64
>Description:
        Transcribed by hand from ddb output:

        uvm_fault(0xffff80004e7e8a30, 0x0, 1) -> e
        fatal page fault in supervisor mode
        trap type 6 code 0 rip ffffffff803ded94 cs 8 rflags 10286 cr2 40 cpl 0 
rsp ffff8000437cd6f0
        kernel: page fault trap, code 0
        Stopped in pid 479.1 (netstat) at netbsd:kath_cred_getuid + 0x4: movl 0 
x40 (%rdi), %eax
>How-To-Repeat:
        Was observing no reponse on network socket (which should
        have held data), then ran netstat. Seems to be a specific
        test case which generates fault, which I can elaborate on
        offline if required.

        On the same host, I was listening on a socket, writing to it,
        observing no response, then ran netstat and crashed the system.

>Fix: