CVE-2022-49377

In the Linux kernel, the following vulnerability has been resolved:

blk-mq: don't touch ->tagset in blkmqgetsqhctx

blkmqrunhwqueues() could be run when there isn't queued request and after queue is cleaned up, at that time tagset is freed, because tagset lifetime is covered by driver, and often freed after blkcleanupqueue() returns.

So don't touch ->tagset for figuring out current default hctx by the mapping built in request queue, so use-after-free on tagset can be avoided. Meantime this way should be fast than retrieving mapping from tagset.