There is no usage of 'nr_expired'.
The 'nr_expired' was introduced by commit 
1d9bd5161ba3 ("blk-mq: replace
timeout synchronization with a RCU and generation based scheme"). Its usage
was removed since commit 
12f5b9314545 ("blk-mq: Remove generation
seqeunce").
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
        unsigned int            queue_num;
 
        atomic_t                nr_active;
-       unsigned int            nr_expired;
 
        struct hlist_node       cpuhp_dead;
        struct kobject          kobj;