It seems that qmt_pool_lookup() jumps to out_err label if qti_pools_add() fails, but the pool lock is not released:

out_err:
        CERROR("%s: cannot add pool %s: err = %d\n",
                qmt->qmt_svname, pos->qpi_name, rc);
        RETURN(ERR_PTR(rc));

seems like a bug?
Introduced by 09f9fb3211c "LU-11023 quota: quota pools for OSTs"