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Date:	Mon, 8 Dec 2014 21:39:22 -0700
From:	Jens Axboe <axboe@...com>
To:	Ming Lei <ming.lei@...onical.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] blk-mq: prevent unmapped hw queue from being scheduled

On 12/08/2014 05:41 PM, Ming Lei wrote:
> On Wed, Dec 3, 2014 at 7:38 PM, Ming Lei <ming.lei@...onical.com> wrote:
>> When one hardware queue has no mapped software queues, it
>> shouldn't have been scheduled. Otherwise WARNING or OOPS
>> can triggered.
>>
>> blk_mq_hw_queue_mapped() helper is introduce for fixing
>> the problem.
>>
>> Signed-off-by: Ming Lei <ming.lei@...onical.com>
>> ---
>>   block/blk-mq.c |    8 ++++++--
>>   block/blk-mq.h |    5 +++++
>>   2 files changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index c95abc6..c916ad0 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -599,7 +599,7 @@ static void blk_mq_rq_timer(unsigned long priv)
>>                   * If not software queues are currently mapped to this
>>                   * hardware queue, there's nothing to check
>>                   */
>> -               if (!hctx->nr_ctx || !hctx->tags)
>> +               if (!blk_mq_hw_queue_mapped(hctx))
>>                          continue;
>>
>>                  blk_mq_tag_busy_iter(hctx, blk_mq_check_expired, &data);
>> @@ -819,7 +819,8 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
>>
>>   void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
>>   {
>> -       if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
>> +       if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state) ||
>> +           !blk_mq_hw_queue_mapped(hctx)))
>>                  return;
>>
>>          if (!async) {
>> @@ -926,6 +927,9 @@ static void blk_mq_delay_work_fn(struct work_struct *work)
>>
>>   void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
>>   {
>> +       if (unlikely(!blk_mq_hw_queue_mapped(hctx)))
>> +               return;
>> +
>>          kblockd_schedule_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
>>                          &hctx->delay_work, msecs_to_jiffies(msecs));
>>   }
>> diff --git a/block/blk-mq.h b/block/blk-mq.h
>> index d567d52..206230e 100644
>> --- a/block/blk-mq.h
>> +++ b/block/blk-mq.h
>> @@ -115,4 +115,9 @@ static inline void blk_mq_set_alloc_data(struct blk_mq_alloc_data *data,
>>          data->hctx = hctx;
>>   }
>>
>> +static inline bool blk_mq_hw_queue_mapped(struct blk_mq_hw_ctx *hctx)
>> +{
>> +       return hctx->nr_ctx && hctx->tags;
>> +}
>> +
>>   #endif
>
> Gentle ping...

Picked up for 3.19, sorry for the delay. I'm curious how this queue gets 
scheduled, though. My worry here would be that we are masking a bug that 
should be fixed separately.

-- 
Jens Axboe

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