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NFS client fails to mount with timeout on kernel 5.4.0-1057-aws

bo flag

On an Ubuntu 18.04.1 server, I am able mount AWS EFS filesystems with nfsv4.1 successfully.

Mounts work on kernel version 5.4.0-1056-aws but if i upgrade the kernel to 5.4.0-1057-aws the mounts stop working with a network timeout, due to port 111 being blocked (as its not needed for nfsv4.1)

Issue started to happen when apt daily automatically upgraded the kernel version.

I reproduced by rolling back kernel version on the same instance and doing mounts successfully, then reverting to newer kernel (plus reboot) and getting the network timeout issue again.

Mount command is identical in all cases and follows AWS Documentation

sudo mount -t nfs -o nfsvers=4.1,rsize=1048576,wsize=1048576,hard,timeo=600,retrans=2,noresvport mount-target-DNS:/   ~/efs-mount-point  

and have confirmed its not a network issue as i'm able to do mounts successfully on the previous kernel.

Could it be a kernel bug or misconfiguration ?

in flag
The AWS-specific kernels are created by Amazon for Amazon hardware. You may want to ask them whether they’ve introduced the issue on purpose or accidentally
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