Jeff Layton writes via Kernel.org Bugzilla:

Li Lingfeng's analysis looks basically correct to me, though I think the nfsd_mutex is mostly a red-herring here.

The client holds the shrinker rwsem and is trying to write back data. The server is trying to unregister a shrinker as part of server shutdown and has almost certainly stopped responding to requests at that point. The client is using hard RPCs, so it's going to retry the writeback indefinitely while holding the shrinker mutex, which will block server shutdown.

I don't see a great way to fix this right offhand, though I wonder if localio might help mitigate this problem.

View: https://bugzilla.kernel.org/show_bug.cgi?id=219550#c4
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