This issue was found in 4.14 and is present in earlier kernels. Please backport f5bbbbe4d635 blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter 530ca2c9bd69 blk-mq: Allow blocking queue tag iter callbacks onto the stable branches that don't have these. The second is a fix for the first. Thank you. 4.19.y and later - commits already present 4.14.y - f5bbbbe4d635 doesn't patch cleanly but it's still straightforward, just drop the comment and code mentioning switching to 'none' in the trailing context 4.9.y - ditto 4.4.y - there was a refactoring of the code in commit 0bf6cd5b9531bcc29c0a5e504b6ce2984c6fd8d8 making this non-trivial 3.16.y - ditto I am happy to try to produce clean patches, but it may be a day or so. Regards, Giuliano.
