linux-kernel - Re: [PATCH 7/8] mq-deadline: add blk-mq adaptation of the deadline IO scheduler

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Date:   Wed, 21 Dec 2016 11:59:28 +0000
From:   Bart Van Assche <Bart.VanAssche@...disk.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "axboe@...com" <axboe@...com>, "axboe@...nel.dk" <axboe@...nel.dk>
CC:     "osandov@...com" <osandov@...com>,
        "paolo.valente@...aro.org" <paolo.valente@...aro.org>
Subject: Re: [PATCH 7/8] mq-deadline: add blk-mq adaptation of the deadline
 IO scheduler

On 12/17/2016 01:12 AM, Jens Axboe wrote:
> +static bool dd_put_request(struct request *rq)
> +{
> +	/*
> +	 * If it's a real request, we just have to
free it. For a shadow
> +	 * request, we should only free it if we haven't started it. A
> +	 * started request is mapped to a real one, and the
real one will
> +	 * free it. We can get here with request merges, since we then
> +	 * free the request before we start/issue it.
> +	 */
> +	
if (!blk_mq_sched_rq_is_shadow(rq))
> +		return false;
> +
> +	if (!(rq->rq_flags & RQF_STARTED)) {
> +		struct request_queue *q
= rq->q;
> +		struct deadline_data *dd = q->elevator->elevator_data;
> +
> +		/*
> +		 * IO completion would normally do
this, but if we merge
> +		 * and free before we issue the request, drop both the
> +		 * tag and queue ref
> +		 */
> +	
	blk_mq_sched_free_shadow_request(dd->tags, rq);
> +		blk_queue_exit(q);
> +	}
> +
> +	return true;
> +}

Hello Jens,

Since this patch is the first patch that introduces a call to blk_queue_exit()
from a module other than the block layer core, shouldn't this patch export the
blk_queue_exit() function? An attempt to build mq-deadline as a module resulted
in the following:

ERROR: "blk_queue_exit" [block/mq-deadline.ko] undefined!
make[1]: *** [scripts/Makefile.modpost:91: __modpost] Error 1
make: *** [Makefile:1198: modules] Error 2
Execution failed: make all

Bart.