Re: Debugging kernel semaphore contention and priority inversion

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will netconsole install on mandriva?


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

-----Original Message-----
From: Mike Galbraith [mailto:[email protected]]
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 | [email protected]
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