Re: copy_file_range() infinitely hangs on NFSv4.2 over RDMA

[Chuck Lever <chuck.lever@oracle.com>]

> On Feb 20, 2021, at 4:03 PM, Timo Rothenpieler <timo@rothenpieler.org> wrote:
> 
> On 19.02.2021 19:48, Chuck Lever wrote:
>>> On Feb 19, 2021, at 1:01 PM, Timo Rothenpieler <timo@rothenpieler.org> wrote:
>>> 
>>> On 19.02.2021 18:48, Chuck Lever wrote:
>>>>> On Feb 19, 2021, at 12:38 PM, Olga Kornievskaia <aglo@umich.edu> wrote:
>>>>> 
>>>>> On Thu, Feb 18, 2021 at 3:22 PM Timo Rothenpieler <timo@rothenpieler.org> wrote:
>>>>>> 
>>>>>> On 18.02.2021 19:30, Olga Kornievskaia wrote:
>>>>>>> Thank you for getting tracepoints from a busy server but can you get
>>>>>>> more? As suspected, the server is having issues sending the callback.
>>>>>>> I'm not sure why. Any chance to turn on the server's sunrpc
>>>>>>> tracespoints, probably both sunrpc and rdmas tracepoints, I wonder if
>>>>>>> we can any more info about why it's failing?
>>>>>> 
>>>>>> I isolated out two of the machines on that cluster now, one acting as
>>>>>> NFS server from an ext4 mount, the other is the same client as before.
>>>>>> That way I managed to capture a trace and ibdump of an entire cycle:
>>>>>> mount + successful copy + 5 minutes later a copy that got stuck
>>>>>> 
>>>>>> Next to no noise happened during those traces, you can find them attached.
>>>>>> 
>>>>>> Another observation made due to this: unmount and re-mounting the NFS
>>>>>> share also gets it back into working condition for a while, no reboot
>>>>>> necessary.
>>>>>> During this trace, I got "lucky", and after just 5 minutes of waiting,
>>>>>> it got stuck.
>>>>>> 
>>>>>> Before that, I had a run of mount + trying to copy every 5 minutes where
>>>>>> it ran for 45 minutes without getting stuck. At which point I decided to
>>>>>> remount once more.
>>>>> 
>>>>> Timo, thank you for gathering the debug info.
>>>>> 
>>>>> Chuck, I need your help. Why would the server lose a callback channel?
>>>>> 
>>>>>           <...>-1461944 [001] 2076465.200151: rpc_request:
>>>>> task:57752@6 nfs4_cbv1 CB_OFFLOAD (async)
>>>>>           <...>-1461944 [001] 2076465.200151: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE status=0 action=call_reserve
>>>>>           <...>-1461944 [001] 2076465.200154: xprt_reserve:
>>>>> task:57752@6 xid=0x00a0aaf9
>>>>>           <...>-1461944 [001] 2076465.200155: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE status=0 action=call_reserveresult
>>>>>           <...>-1461944 [001] 2076465.200156: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE status=0 action=call_refresh
>>>>>           <...>-1461944 [001] 2076465.200163: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE status=0 action=call_refreshresult
>>>>>           <...>-1461944 [001] 2076465.200163: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE status=0 action=call_allocate
>>>>>           <...>-1461944 [001] 2076465.200168: rpc_buf_alloc:
>>>>> task:57752@6 callsize=548 recvsize=104 status=0
>>>>>           <...>-1461944 [001] 2076465.200168: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE status=0 action=call_encode
>>>>>           <...>-1461944 [001] 2076465.200173: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE|NEED_XMIT|NEED_RECV status=0
>>>>> action=call_connect
>>>>>           <...>-1461944 [001] 2076465.200174: rpc_call_rpcerror:
>>>>> task:57752@6 tk_status=-107 rpc_status=-107
>>>>>           <...>-1461944 [001] 2076465.200174: rpc_task_run_action:
>>>>> task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT
>>>>> runstate=RUNNING|ACTIVE|NEED_XMIT|NEED_RECV status=-107
>>>>> action=rpc_exit_task
>>>>> 
>>>>> It's reporting ENOTCON. I'm not really sure if this is related to copy
>>>>> offload but more perhaps doing callbacks over RDMA/IB.
>>>> If the client is awaiting a COPY notification callback, I can see why
>>>> a lost CB channel would cause the client to wait indefinitely.
>>>> The copy mechanism has to deal with this contingency... Perhaps the
>>>> server could force a disconnect so that the client and server have an
>>>> opportunity to re-establish the callback channel. <shrug>
>>>> In any event, the trace log above shows nothing more than "hey, it's
>>>> not working." Are there any rpcrdma trace events we can look at to
>>>> determine why the backchannel is getting lost?
>>> 
>>> The trace log attached to my previous mail has it enabled, along with nfsd and sunrpc.
>>> I'm attaching the two files again here.
>> Thanks, Timo.
>> The first CB_OFFLOAD callback succeeds:
>> 2076155.216687: nfsd_cb_work:         addr=10.110.10.252:0 client 602eb645:daa037ae procedure=CB_OFFLOAD
>> 2076155.216704: rpc_request:          task:57746@6 nfs4_cbv1 CB_OFFLOAD (async)
>> 2076155.216975: rpc_stats_latency:    task:57746@6 xid=0xff9faaf9 nfs4_cbv1 CB_OFFLOAD backlog=33 rtt=195 execute=282
>> 2076155.216977: nfsd_cb_done:         addr=10.110.10.252:0 client 602eb645:daa037ae status=0
>> About 305 seconds later, the autodisconnect timer fires. I'm not sure if this is the backchannel transport, but it looks suspicious:
>> 2076460.314954: xprt_disconnect_auto: peer=[10.110.10.252]:0 state=LOCKED|CONNECTED|BOUND
>> 2076460.314957: xprt_disconnect_done: peer=[10.110.10.252]:0 state=LOCKED|CONNECTED|BOUND
>> The next CB_OFFLOAD callback fails because the xprt has been marked "disconnected" and the request's NOCONNECT flag is set.
>> 2076465.200136: nfsd_cb_work:         addr=10.110.10.252:0 client 602eb645:daa037ae procedure=CB_OFFLOAD
>> 2076465.200151: rpc_request:          task:57752@6 nfs4_cbv1 CB_OFFLOAD (async)
>> 2076465.200168: rpc_task_run_action:  task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT runstate=RUNNING|ACTIVE status=0 action=call_encode
>> 2076465.200173: rpc_task_run_action:  task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT runstate=RUNNING|ACTIVE|NEED_XMIT|NEED_RECV status=0 action=call_connect
>> 2076465.200174: rpc_call_rpcerror:    task:57752@6 tk_status=-107 rpc_status=-107
>> 2076465.200174: rpc_task_run_action:  task:57752@6 flags=ASYNC|DYNAMIC|SOFT|NOCONNECT runstate=RUNNING|ACTIVE|NEED_XMIT|NEED_RECV status=-107 action=rpc_exit_task
>> 2076465.200179: nfsd_cb_done:         addr=10.110.10.252:0 client 602eb645:daa037ae status=-107
>> 2076465.200180: nfsd_cb_state:        addr=10.110.10.252:0 client 602eb645:daa037ae state=FAULT
>> Perhaps RPC clients for NFSv4.1+ callback should be created with
>> the RPC_CLNT_CREATE_NO_IDLE_TIMEOUT flag.
> 
> I added that flag to the callback client creation flags, and so far after a few hours of uptime, copying still works.

It seems like a good thing to do in any event (barring any other observations).
Can you send a patch for review?


> Can't say anything about that being the appropriate fix for the issue at hand, as I lack the necessary insight into the NFS code, but I'll leave it running like that for now and observe.
> 
> Can also gladly test any other patches.
> 
> 
> Thanks,
> Timo

--
Chuck Lever