linux-kernel - Re: [PATCH] blk-mq: fix blk_mq_start_stopped_hw

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Date:	Sun, 6 Oct 2013 12:10:13 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: fix blk_mq_start_stopped_hw_queues from irq
 context

On Sun, Oct 06 2013, Christoph Hellwig wrote:
> The only caller of blk_mq_start_stopped_hw_queues is in irq context,
> leading to lockdep splat when it actually gets called.  Fix this by
> deferring the hw queue run to workqueue context.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2b85029..923e9e1 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -686,7 +686,8 @@ void blk_mq_start_stopped_hw_queues(struct request_queue *q)
>  		if (!test_bit(BLK_MQ_S_STOPPED, &hctx->state))
>  			continue;
>  
> -		blk_mq_start_hw_queue(hctx);
> +		clear_bit(BLK_MQ_S_STOPPED, &hctx->state);
> +		blk_mq_run_hw_queue(hctx, true);
>  	}
>  }
>  EXPORT_SYMBOL(blk_mq_start_stopped_hw_queues);

Thanks, applied. Might not be a bad idea to just mimic the run queue
API, and provide a blk_mq_start_hw_queue(hctx, is_async) instead.

-- 
Jens Axboe

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