Re: [PATCH 0/5] blk-mq: allow to run queue if queue refcount is held

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Hi Ming

On 4/1/19 10:52 AM, Ming Lei wrote:
>> percpu_ref_tryget_live() fails if a per-cpu counter is in the "dead" state.
>> percpu_ref_kill() changes the state of a per-cpu counter to the "dead"
>> state. blk_freeze_queue_start() calls percpu_ref_kill(). blk_cleanup_queue()
>> already calls blk_set_queue_dying() and that last function calls
>> blk_freeze_queue_start(). So I think that what you wrote is not correct and
>> that inserting a percpu_ref_tryget_live()/percpu_ref_put() pair in
>> blk_mq_run_hw_queues() or blk_mq_run_hw_queue() would make a difference and
>> also that moving the percpu_ref_exit() call into blk_release_queue() makes
>> sense.
> If percpu_ref_exit() is moved to blk_release_queue(), we still need to
> move freeing of hw queue's resource into blk_release_queue() like what
> the patchset is doing.
> 
> Then we don't need to get/put q_usage_counter in blk_mq_run_hw_queues() any more,
> do we?

IMO, if we could get a way to prevent any attempt to run queue, it would be
better and clearer.

Thanks
Jianchao



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