Re: Hard hangs on AMD64 with mpsafenet enabled

Robert Watson <rwatson_at_freebsd.org> writes:

> Thanks for the report -- I have some questions below that it would be
> helpful if you could answer.
>
> On Tue, 26 Oct 2004, [iso-8859-2] Sławek Żak wrote:
>
>>     I've got a Sun V20z 2 cpu Opteron box. I experience hard hangs when
>>     accessing NFS simulatneously from 2 processes (tested with parallel port
>>     builds with /usr/ports mounted over NFS with
>>     nosuid,nodev,soft,bg,intr). rpc.lockd and rpc.statd are both enabled for
>>     NFS.
>
> From the above, can I assume that this is a problem on the NFS client, and
> that the NFS server is on another system reachable via a local area
> network?

    Correct.
    
> When "hung", can the machine be pinged from another machine?

    Haven't tried it. I will.
    
> From your subject line, it looks like you mean "when debug.mpsafenet=0,
> this doesn't happen".  Is that a correct reading?

    Yes, I've forgotten to add it, but followed up with another email.
    
> Could you try running with WITNESS and INVARIANTS enabled, and see if you
> get any specific warnings or assertion failures?  A hard hang could imply
> a deadlock, which WITNESS would be able to report on.  Other sources of
> hard hangs may be easier to debug with INVARIANTS and WITNESS enabled.

    Ok.
    
> If possible, getting access to a serial console might make this problem
> significantly easier to debug.

    I will try to make a cable for such access. Tomorrow morning.
    
>>     I cannot also enter the debugger with C-M-ESC (no serial console at this
>>     moment, sorry). When the system is running and I try to enter the debugger
>>     on video console I get garbage on the screen and a reboot immediately
>>     after. Scary stuff. I can't play with MP watchdog now (4 CPU box arrives in
>>     two weeks).
>
> So when there isn't a problem and you try to enter the debugger on the
> video console, you get the garbage, or only when this problem is
> manifesting? 

    When the server is working fine. When it's hanging I cannot enter the
    debugger.

/S