In the Linux kernel, the following vulnerability has been resolved:
NFSD: fix hang in nfsd4shutdowncallback
If nfs4client is in courtesy state then there is no point to send the callback. This causes nfsd4shutdowncallback to hang since clcb_inflight is not 0. This hang lasts about 15 minutes until TCP notifies NFSD that the connection was dropped.
This patch modifies nfsd4runcbwork to skip the RPC call if nfs4client is in courtesy state.