Description: NFSD: fix use-after-free in nfsd4_ssc_setup_dul()
References:
 https://bugzilla.redhat.com/show_bug.cgi?id=2182031
Notes:
 carnil> Commit fixes f4e44b393389 ("NFSD: delay unmount source's export
 carnil> after inter-server copy completed.") in 5.14-rc1.
Bugs:
upstream: released (6.2-rc5) [e6cf91b7b47ff82b624bdfe2fdcde32bb52e71dd]
6.1-upstream-stable: released (6.1.9) [32d5eb95f8f0e362e37c393310b13b9e95404560]
5.10-upstream-stable: N/A "Vulnerable code not present"
4.19-upstream-stable: N/A "Vulnerable code not present"
sid: released (6.1.11-1)
5.10-bullseye-security: N/A "Vulnerable code not present"
4.19-buster-security: N/A "Vulnerable code not present"