DUMP processing holds the VTOC resource while dumping a volume. Whenever DUMP processing reaches the EOV, it must get the TIOT resource in order to access a new tape. However if a request is issued to allocate a data set on the DASD being dumped, the request holds the TIOT resource and requests the VTOC resource instead. This inverse ordering of resource acquisition can result in a function deadlock.

PATCH .MCVT.+3C3 BITS(.....1..)

You can also activate early VTOC release by invoking the ADRUENQ installation exit. See z/OS DFSMS Installation Exits for more information on the ADRUENQ installation exit.