Re: Debugging kernel semaphore contention and priority inversion

[Hal Wigoda]

will netconsole install on mandriva?


On Aug 18, 2005, at 9:50 AM, Davda, Bhavesh P ((Bhavesh)) wrote:

> > -----Original Message-----
> > From: Mike Galbraith [mailto:efault@xxxxxx]
> > Sent: Wednesday, August 17, 2005 11:10 PM
> > At 09:43 PM 8/17/2005 -0600, you wrote:
> > > > Have you tried sysrq t?  See the Documentation/sysrq.txt file.
> > >
> > > This is a headless system.
> >
> > You could try netconsole.
>
> Haven't heard of it before. Will look into it. But I doubt it will help
> pinpoint the semaphore holder, if all I can do is sysrq stuff.
>
> > > > How stuck is the system?
> > > >
> > > > Keith
> > >
> > > Very. Only pingable, but can't login via
> > telnet/ssh/anything. Reason is
> > > the same reason the low priority mystery task is unable to run and
> > > release the held semaphore.
> >
> > (hmm.  I'm obviously missing some original context here)
> >
> > Sounds like there must be another player who is RT prio + spinning.
> >
> >          -Mike
>
> Very good! Yes, I left out that piece of detail in my original posting.
> There is a real low priority (4) SCHED_FIFO (hence still higher than 
> any
> SCHED_OTHER) task spinning. But it is not the semaphore holder. I am
> trying to identify which kernel thread (because that's most likely)
> running at SCHED_OTHER real low priority (too nice) is holding the
> semaphore, locking out a priority 50 SCHED_FIFO task in its sys_write()
> as a result.
>
> Thanks
>
> - Bhavesh
>
> Bhavesh P. Davda | Distinguished Member of Technical Staff | Avaya |
> 1300 West 120th Avenue | B3-B03 | Westminster, CO 80234 | U.S.A. |
> Voice/Fax: 303.538.4438 | bhavesh@xxxxxxxxx
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