block: fix q->blkg_list corruption during disk rebind

In the Linux kernel, the following vulnerability has been resolved: block: fix q->blkg_list corruption during disk rebind Multiple gendisk instances can allocated/added for single request queue in case of disk rebind. blkg may still stay in q->blkg_list when calling blkcg_init_disk() for rebind, then q->blkg_list becomes corrupted. Fix the list corruption issue by: - add blkg_init_queue() to initialize q->blkg_list & q->blkcg_mutex only - move calling blkg_init_queue() into blk_alloc_queue() The list corruption should be started since commit f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()") which delays removing blkg from q->blkg_list into blkg_free_workfn().