[gpfsug-discuss] strange waiters + filesystem deadlock

[Sven Oehme]

while this is happening  run top and see if there is very high cpu
utilization at this time on the NSD Server.

if there is , run perf top (you might need to install perf command) and see
if the top cpu contender is a spinlock . if so send a screenshot of perf
top as i may know what that is and how to fix.

sven

On Fri, Mar 24, 2017 at 9:43 AM Aaron Knister <aaron.s.knister at nasa.gov>
wrote:

> 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
>
> --
> Aaron Knister
> NASA Center for Climate Simulation (Code 606.2)
> Goddard Space Flight Center
> (301) 286-2776
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>
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