linux-kernel - Re: [PATCH] blk-mq: Put driver tag in blk_mq_dispatch_rq

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Message-ID: <20200416141216.GA2907988@T590>
Date:   Thu, 16 Apr 2020 22:12:16 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: Put driver tag in blk_mq_dispatch_rq_list() when
 no budget

On Thu, Apr 16, 2020 at 07:18:51PM +0800, John Garry wrote:
> If in blk_mq_dispatch_rq_list() we find no budget, then we break of the
> dispatch loop, but the request may keep the driver tag, evaulated
> in 'nxt' in the previous loop iteration.
> 
> Fix by putting the driver tag for that request.
> 
> Signed-off-by: John Garry <john.garry@...wei.com>
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8e56884fd2e9..a7785df2c944 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1222,8 +1222,10 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
>  		rq = list_first_entry(list, struct request, queuelist);
>  
>  		hctx = rq->mq_hctx;
> -		if (!got_budget && !blk_mq_get_dispatch_budget(hctx))
> +		if (!got_budget && !blk_mq_get_dispatch_budget(hctx)) {
> +			blk_mq_put_driver_tag(rq);
>  			break;
> +		}
>  
>  		if (!blk_mq_get_driver_tag(rq)) {
>  			/*
> -- 
> 2.16.4
> 

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

-- 
Ming