linux-kernel - Re: [PATCH] blk-mq: clear active_queues before clearing BLK_MQ_F_TAG_QUEUE

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Message-ID: <YQydfkffPhBEFpwB@T590>
Date:   Fri, 6 Aug 2021 10:25:02 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH] blk-mq: clear active_queues before clearing
 BLK_MQ_F_TAG_QUEUE_SHARED

On Sat, Jul 31, 2021 at 02:21:30PM +0800, Yu Kuai wrote:
> We run a test that delete and recover devcies frequently(two devices on
> the same host), and we found that 'active_queues' is super big after a
> period of time.
> 
> If device a and device b share a tag set, and a is deleted, then
> blk_mq_exit_queue() will clear BLK_MQ_F_TAG_QUEUE_SHARED because there
> is only one queue that are using the tag set. However, if b is still
> active, the active_queues of b might never be cleared even if b is
> deleted.
> 
> Thus clear active_queues before BLK_MQ_F_TAG_QUEUE_SHARED is cleared.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
>  block/blk-mq.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2c4ac51e54eb..2fe396385a4a 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2994,10 +2994,12 @@ static void queue_set_hctx_shared(struct request_queue *q, bool shared)
>  	int i;
>  
>  	queue_for_each_hw_ctx(q, hctx, i) {
> -		if (shared)
> +		if (shared) {
>  			hctx->flags |= BLK_MQ_F_TAG_QUEUE_SHARED;
> -		else
> +		} else {
> +			blk_mq_tag_idle(hctx);
>  			hctx->flags &= ~BLK_MQ_F_TAG_QUEUE_SHARED;
> +		}
>  	}
>  }

Looks correct, the only remained queue in tagset has to be idled before
clearing BLK_MQ_F_TAG_QUEUE_SHARED:

Reviewed-by: Ming Lei <ming.lei@...hat.com>



Thanks,
Ming