[PLUG] killing "D" state processes?

Shannon C. Dealy dealy at deatech.com
Tue May 14 22:38:28 UTC 2002


On 14 May 2002, Russell Senior wrote:

>
> I've been having a little trouble with a backup process.  This morning
> an 'mt' hung on me in a "D N" state, which according to "man ps"
> decodes as Wing Attack Plan R, R for Robert ... Oops!  No, sorry.
> Those weren't today's codes.  It decodes as D = "uninterruptible sleep
> (usually IO)" and N = "low-priority task".  A "kill -9 <pid>" doesn't
> work.  The tape wasn't moving, I ejected the tape and reinserted it,
> but mt is still stuck.  Do I have to reboot the sucker?  Or is there
> some incantation like: "Peace on Earth" or "Purity of Essense" to fix
> it?

I used to get these years ago during tape backups (including the failure
of the kill -9), it turned out to be a kernel bug/race condition that
would happen on rare occasions, but as far as I can recall, it only
happened to me on pre 2.2 kernels.  The only possible cure for my problem
when I tracked down the cause was in fact a reboot, because (if I remember
correctly), the kernel code that was doing the I/O where it locked up was
coded incorrectly and did not allow for any kills in the loop where it
was waiting for an I/O event that would never come because of the race
condition.  What kernel version are you running?

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
                      |    Embedded Systems, Real-time, Device Drivers
Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
   or: (541) 451-5177 |                  www.deatech.com





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