[PATCH V2] nvme: free pre-allocated queue if create ioq goes wrong

[jianchao.wang]

Hi Minwoo 

On 01/17/2018 11:00 PM, Minwoo Im wrote:
> On Mon, Jan 15, 2018 at 11:00 AM, Keith Busch <keith.busch at intel.com> wrote:
>> Unless this is the very first pass at initialisation, I don't think we
>> can free queues until after blk_mq_update_nr_hw_queues since the hctx
>> could otherwise point to freed memory.
> 
> If not in the first initial step, if (_online_queues_ < 2) driver will
> kill queues and
> remove namespaces. I thought this "killing queue" will handle what you concerned
> about. If I misunderstand what it is, please let me know.
> Think of the following scenario:
nvme_reset_work
  -> nvme_setup_io_queues
    -> nvme_create_io_queues
      -> nvme_free_queues
  -> nvme_kill_queues
    -> blk_set_queue_dying   // just freeze the queue here, but will not wait to be drained.
                                not new requests come in, but maybe still residual requests in blk-mq queues.
    -> blk_mq_unquiesce_queue

the queues are _unquiesced_ here, then the residual requests will be queued
and go through nvme_queue_rq. Then the freed nvme_queue structure will be accessed.
:)

Thanks
Jianchao

> Otherwise if (_online_queues_ >= 2) which means that
> at least one or more IO queue is prepared, blk_mq_update_nr_hw_queues()
> will be triggered as you said.
> 
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