[gpfsug-discuss] strange waiters + filesystem deadlock

[Fosburgh,Jonathan]

This is one of the more annoying long waiter problems. We've seen it several times and I'm not sure they all had the same cause.

What version of GPFS?
Do you have anything like Tivoli HSM or LTFSEE?

--

Jonathan Fosburgh
Principal Application Systems Analyst
Storage Team
IT Operations
jfosburg at mdanderson.org<mailto:jfosburg at mdanderson.org>
(713) 745-9346

-----Original Message-----

Date: Fri, 24 Mar 2017 12:43:02 -0400
Subject: [gpfsug-discuss] strange waiters + filesystem deadlock
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org<mailto:gpfsug%20main%20discussion%20list%20%3cgpfsug-discuss at spectrumscale.org%3e>>
Reply-to: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
From: Aaron Knister <aaron.s.knister at nasa.gov<mailto:Aaron%20Knister%20%3caaron.s.knister at nasa.gov%3e>>

Since yesterday morning we've noticed some deadlocks on one of our
filesystems that seem to be triggered by writing to it. The waiters on
the clients look like this:

0x19450B0 (   6730) waiting 2063.294589599 seconds, SyncHandlerThread:
on ThCond 0x1802585CB10 (0xFFFFC9002585CB10) (InodeFlushCondVar), reason
'waiting for the flush flag to commit metadata'
0x7FFFDA65E200 (  22850) waiting 0.000246257 seconds,
AllocReduceHelperThread: on ThCond 0x7FFFDAC7FE28 (0x7FFFDAC7FE28)
(MsgRecordCondvar), reason 'RPC wait' for allocMsgTypeRelinquishRegion
on node 10.1.52.33 <c0n3271>
0x197EE70 (   6776) waiting 0.000198354 seconds,
FileBlockWriteFetchHandlerThread: on ThCond 0x7FFFF00CD598
(0x7FFFF00CD598) (MsgRecordCondvar), reason 'RPC wait' for
allocMsgTypeRequestRegion on node 10.1.52.33 <c0n3271>

(10.1.52.33/c0n3271 is the fs manager for the filesystem in question)

there's a single process running on this node writing to the filesystem
in question (well, trying to write, it's been blocked doing nothing for
half an hour now). There are ~10 other client nodes in this situation
right now. We had many more last night before the problem seemed to
disappear in the early hours of the morning and now its back.

Waiters on the fs manager look like this. While the individual waiter is
short it's a near constant stream:

0x7FFF60003540 (   8269) waiting 0.001151588 seconds, Msg handler
allocMsgTypeRequestRegion: on ThMutex 0x1802163A2E0 (0xFFFFC9002163A2E0)
(AllocManagerMutex)
0x7FFF601C8860 (  20606) waiting 0.001115712 seconds, Msg handler
allocMsgTypeRelinquishRegion: on ThMutex 0x1802163A2E0
(0xFFFFC9002163A2E0) (AllocManagerMutex)
0x7FFF91C10080 (  14723) waiting 0.000959649 seconds, Msg handler
allocMsgTypeRequestRegion: on ThMutex 0x1802163A2E0 (0xFFFFC9002163A2E0)
(AllocManagerMutex)
0x7FFFB03C2910 (  12636) waiting 0.000769611 seconds, Msg handler
allocMsgTypeRequestRegion: on ThMutex 0x1802163A2E0 (0xFFFFC9002163A2E0)
(AllocManagerMutex)
0x7FFF8C092850 (  18215) waiting 0.000682275 seconds, Msg handler
allocMsgTypeRelinquishRegion: on ThMutex 0x1802163A2E0
(0xFFFFC9002163A2E0) (AllocManagerMutex)
0x7FFF9423F730 (  12652) waiting 0.000641915 seconds, Msg handler
allocMsgTypeRequestRegion: on ThMutex 0x1802163A2E0 (0xFFFFC9002163A2E0)
(AllocManagerMutex)
0x7FFF9422D770 (  12625) waiting 0.000494256 seconds, Msg handler
allocMsgTypeRequestRegion: on ThMutex 0x1802163A2E0 (0xFFFFC9002163A2E0)
(AllocManagerMutex)
0x7FFF9423E310 (  12651) waiting 0.000437760 seconds, Msg handler
allocMsgTypeRelinquishRegion: on ThMutex 0x1802163A2E0
(0xFFFFC9002163A2E0) (AllocManagerMutex)

I don't know if this data point is useful but both yesterday and today
the metadata NSDs for this filesystem have had a constant aggregate
stream of 25MB/s 4kop/s reads during each episode (very low latency
though so I don't believe the storage is a bottleneck here). Writes are
only a few hundred ops and didn't strike me as odd.

I have a PMR open for this but I'm curious if folks have seen this in
the wild and what it might mean.

-Aaron


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