Re: [PATCH] block: drain queue before waiting for q_usage_counter becoming zero

[Hannes Reinecke <hare@suse.de>]

On 11/22/2017 06:11 AM, Ming Lei wrote:
> Now we track legacy requests with .q_usage_counter in commit 055f6e18e08f
> ("block: Make q_usage_counter also track legacy requests"), but that
> commit never runs and drains legacy queue before waiting for this counter
> becoming zero, then IO hang is caused in the test of pulling disk during IO.
> 
> This patch fixes the issue by draining requests before waiting for
> q_usage_counter becoming zero.
> 
> Fixes: 055f6e18e08f("block: Make q_usage_counter also track legacy requests")
> Cc: Wen Xiong <wenxiong@us.ibm.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  block/blk-core.c | 9 +++++++--
>  block/blk-mq.c   | 2 ++
>  block/blk.h      | 2 ++
>  3 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 1038706edd87..5ae5ea0dca4c 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -562,6 +562,13 @@ static void __blk_drain_queue(struct request_queue *q, bool drain_all)
>  	}
>  }
>  
> +void blk_drain_queue(struct request_queue *q)
> +{
> +	spin_lock_irq(q->queue_lock);
> +	__blk_drain_queue(q, true);
> +	spin_unlock_irq(q->queue_lock);
> +}
> +
>  /**
>   * blk_queue_bypass_start - enter queue bypass mode
>   * @q: queue of interest
> @@ -689,8 +696,6 @@ void blk_cleanup_queue(struct request_queue *q)
>  	 */
>  	blk_freeze_queue(q);
>  	spin_lock_irq(lock);
> -	if (!q->mq_ops)
> -		__blk_drain_queue(q, true);
>  	queue_flag_set(QUEUE_FLAG_DEAD, q);
>  	spin_unlock_irq(lock);
>  
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 11097477eeab..3d3797327491 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -161,6 +161,8 @@ void blk_freeze_queue(struct request_queue *q)
>  	 * exported to drivers as the only user for unfreeze is blk_mq.
>  	 */
>  	blk_freeze_queue_start(q);
> +	if (!q->mq_ops)
> +		blk_drain_queue(q);
>  	blk_mq_freeze_queue_wait(q);
>  }
>  
> diff --git a/block/blk.h b/block/blk.h
> index 3f1446937aec..442098aa9463 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -330,4 +330,6 @@ static inline void blk_queue_bounce(struct request_queue *q, struct bio **bio)
>  }
>  #endif /* CONFIG_BOUNCE */
>  
> +extern void blk_drain_queue(struct request_queue *q);
> +
>  #endif /* BLK_INTERNAL_H */
> 
I seem to have missed something.
Is blk_drain_queue() ever used?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
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