nfs4_schedule_state_manager stuck in tight loop

[Christian Theune]

Hi,

unfortunately I’m a bit light on details, but willing to provide better diagnostics as this moves along.

We’ve had two instances of NFS clients getting stuck with a kernel thread spinning around `nfs4_schedule_state_manager` AFAICT:

The first instance of this was last September on a Qemu VM running a 6.1.45 guest:

root 315344 44.5 0.0 0 0 ? D Sep05 781:38 \_ [172.22.56.83-manager]

It happened a second time in last December on another VM that was likely running 5.15.139. (We downgraded our fleet due to other stability issues from 6.1 to 5.15 in between those two incidents.)

My colleagues told me that no issues were visible in the logs at that time, the systems were generally usable but interacting with anything on NFS was (obviously) stuck. So apparently no (soft-) lock ups and no stalls were recorded, but I’ll ask my colleagues to either alert me or provide all of the logging they can get the next time this happens.

Cheers,
Christian

PS: I’ve also recorded this in https://bugzilla.kernel.org/show_bug.cgi?id=217877 but switching to mail-based workflow now.

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