[BUG] Deadlock in blk_mq_register_disk error path

[Jinpu Wang]

Hi Jens,

I found in blk_mq_register_disk, we blk_mq_disable_hotplug which in
turn mutex_lock(&all_q_mutex);
  queue_for_each_hw_ctx(q, hctx, i) {
                ret = blk_mq_register_hctx(hctx);
                if (ret)
                        break; /// if about error out, we will call
unregister below
        }

        if (ret)
                blk_mq_unregister_disk(disk);

In blk_mq_unregister_disk, we will try to disable_hotplug again, which
leads to dead lock.

Did I miss anything?

-- 
Mit freundlichen Grüßen,
Best Regards,

Jack Wang

Linux Kernel Developer Storage
ProfitBricks GmbH  The IaaS-Company.
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