linux-kernel - Re: [PATCH 05/24] io-controller: Modify cfq to make use of flat elevator fair queuing

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Date:	Thu, 30 Jul 2009 17:42:46 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	jens.axboe@...cle.com, nauman@...gle.com, dpshah@...gle.com,
	ryov@...inux.co.jp, guijianfeng@...fujitsu.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	lizf@...fujitsu.com, mikew@...gle.com, fchecconi@...il.com,
	paolo.valente@...more.it, fernando@....ntt.co.jp,
	s-uchida@...jp.nec.com, taka@...inux.co.jp, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, m-ikeda@...jp.nec.com, agk@...hat.com,
	akpm@...ux-foundation.org, peterz@...radead.org
Subject: Re: [PATCH 05/24] io-controller: Modify cfq to make use of flat elevator
 fair queuing

Vivek Goyal wrote:
> @@ -1616,11 +1234,12 @@ static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
>  	struct cfq_data *cfqd = cic->key;
>  	struct cfq_queue *cfqq;
>  	unsigned long flags;
> +	struct request_queue *q = cfqd->queue;

cfqd may be NULL here. We'd better test it before using it.

>  
>  	if (unlikely(!cfqd))
>  		return;
>  
> -	spin_lock_irqsave(cfqd->queue->queue_lock, flags);
> +	spin_lock_irqsave(q->queue_lock, flags);
>  
>  	cfqq = cic->cfqq[BLK_RW_ASYNC];
>  	if (cfqq) {
> @@ -1637,7 +1256,7 @@ static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
>  	if (cfqq)
>  		cfq_mark_cfqq_prio_changed(cfqq);
>  
> -	spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
> +	spin_unlock_irqrestore(q->queue_lock, flags);
>  }
>  
>  static void cfq_ioc_set_ioprio(struct io_context *ioc)


--- block/cfq-iosched.c.orig	2009-07-29 10:22:08.000000000 +0200
+++ block/cfq-iosched.c	2009-07-30 17:25:05.000000000 +0200
@@ -1271,11 +1271,12 @@ static void changed_ioprio(struct io_con
 	struct cfq_data *cfqd = cic->key;
 	struct cfq_queue *cfqq;
 	unsigned long flags;
-	struct request_queue *q = cfqd->queue;
+	struct request_queue *q;
 
 	if (unlikely(!cfqd))
 		return;
 
+	q = cfqd->queue;
 	spin_lock_irqsave(q->queue_lock, flags);
 
 	cfqq = cic->cfqq[BLK_RW_ASYNC];
--
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