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To:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-rdma <linux-rdma@vger.kernel.org>
From:   Timo Rothenpieler <timo@rothenpieler.org>
Subject: Spurious instability with NFSoRDMA under moderate load
Message-ID: <4da3b074-a6be-d83f-ccd4-b151557066aa@rothenpieler.org>
Date:   Sun, 16 May 2021 19:29:50 +0200
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This has happened 3 times so far over the last couple months, and I do=20
not have a clear way to reproduce it.
It happens under moderate load, when lots of nodes read and write from=20
the server. Though not in any super intense way. Just normal program=20
execution, writing of light logs, and other standard tasks.

The issues on the clients manifest in a multitude of ways. Most of the=20
time, random IO operations just fail, rarely hang indefinitely and make=20
the process unkillable.
Another example would be: "Failed to remove=20
'.../.nfs00000000007b03af00000001': Device or resource busy"

Once a client is in that state, the only way to get it back into order=20
is a reboot.

On the server side, a single error cqe is dumped each time this problem=20
happened. So far, I always rebooted the server as well, to make sure=20
everything is back in order. Not sure if that is strictly necessary.

> [561889.198889] infiniband mlx5_0: dump_cqe:272:(pid 709): dump error c=
qe
> [561889.198945] 00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00
> [561889.198984] 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00
> [561889.199023] 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00
> [561889.199061] 00000030: 00 00 00 00 00 00 88 13 08 00 01 13 07 47 67 =
d2

> [985074.602880] infiniband mlx5_0: dump_cqe:272:(pid 599): dump error c=
qe
> [985074.602921] 00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00
> [985074.602946] 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00
> [985074.602970] 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =
00
> [985074.602994] 00000030: 00 00 00 00 00 00 88 13 08 00 01 46 f2 93 0b =
d3

> [1648894.168819] infiniband ibp1s0: dump_cqe:272:(pid 696): dump error =
cqe
> [1648894.168853] 00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=
 00
> [1648894.168878] 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=
 00
> [1648894.168903] 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00=
 00
> [1648894.168928] 00000030: 00 00 00 00 00 00 88 13 08 00 01 08 6b d2 b9=
 d3

These all happened under different Versions of the 5.10 Kernel. The last =

one under 5.10.32 today.

Switching all clients to TCP seems to make NFS works perfectly reliable.

I'm not sure how to read those error dumps, so help there would be=20
appreciated.

Could this be similar to spurious issues you get with UDP, where dropped =

packages cause havoc? Though I would not expect heavy load on IB to=20
cause an error cqe to be logged.


Thanks,
Timo


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