fs/nfs/nfs4client.c in the NFS4 subsystem of the Linux kernel before 5.13.4 has incorrect connection-setup ordering, which allows remote NFSv4 servers to cause a denial of service (hanging of mounts) by arranging for those servers to be unreachable during trunking detection.
Reference and upstream patch:
Created kernel tracking bugs for this issue:
Affects: fedora-all [bug 1992272]
This was fixed for Fedora with the 5.13.4 stable kernel updates.