- This issue caused by race condition between drop thread
and fil_encrypt_thread. fil_encrypt_thread closes
the tablespace if the number of opened files
exceeds innodb_open_files. fil_node_open_file()
closes the tablespace which are open and it doesn't
have pending operations. At that time, InnoDB drop tries
to write the redo log for the file delete operation.
It throws the bad file descriptor error.

- When trying to close the file, InnoDB should check
whether the table is going to be dropped.