Re: Debugging kernel semaphore contention and priority inversion

Hal Wigoda
2005-08-18T15:14:05Z

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@gmx.de]
>> 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@avaya.com
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