CVE-2023-53292

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CVE-2023-53292
In the Linux kernel, the following vulnerability has been resolved:

blk-mq: fix NULL dereference on q->elevator in blk_mq_elv_switch_none

After grabbing q->sysfs_lock, q->elevator may become NULL because of
elevator switch.

Fix the NULL dereference on q->elevator by checking it with lock.