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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] blk: fix a wrong accounting of hd_struct->in_flight
Date: Thu, 14 Oct 2010 16:30:41 -0700	[thread overview]
Message-ID: <20101014233041.GJ2447@linux.vnet.ibm.com> (raw)
In-Reply-To: <4CB6FB30.1000502@kernel.dk>

On Thu, Oct 14, 2010 at 02:44:32PM +0200, Jens Axboe wrote:
> On 2010-10-14 08:07, KOSAKI Motohiro wrote:
> >> @@ -1268,7 +1270,17 @@ static int __make_request(struct request
> >>  		 * not touch req->buffer either...
> >>  		 */
> >>  		req->buffer = bio_data(bio);
> >> +		src_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));
> >>  		req->__sector = bio->bi_sector;
> >> +		dst_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));
> > 
> > I think this is wrong. disk_map_sector_rcu() require
> > rcu read lock held (see function comment). all other call site take 
> > part_stat_lock() before disk_map_sector_rcu() call.
> 
> It's called under the queue lock with irqs disabled, which implies a
> rcu critical section.

Having irqs disabled does imply an rcu_read_lock_sched() or an
rcu_read_lock_bh(), but not an rcu_read_lock(), especially if
CONFIG_PREEMPT_RCU.

So an explicit rcu_read_lock() does seem to be needed here.

							Thanx, Paul

  reply	other threads:[~2010-10-14 23:30 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-10-12  6:38 [PATCH] blk: fix a wrong accounting of hd_struct->in_flight Yasuaki Ishimatsu
2010-10-12  8:19 ` Jens Axboe
2010-10-14 12:48   ` [PATCH v2] " Yasuaki Ishimatsu
2010-10-14 12:55     ` Jens Axboe
2010-10-15  8:39       ` [PATCH v3] " Yasuaki Ishimatsu
2010-10-15 10:04         ` Jens Axboe
2010-10-18  8:28           ` [PATCH v4] " Yasuaki Ishimatsu
2010-10-18  8:34             ` Jens Axboe
2010-10-18 12:19               ` [PATCH v5] " Yasuaki Ishimatsu
2010-10-18 12:21                 ` Jens Axboe
2010-10-19  2:22                   ` Yasuaki Ishimatsu
2010-10-19 10:02                     ` Jens Axboe
2010-10-14  6:07 ` [PATCH] " KOSAKI Motohiro
2010-10-14 12:44   ` Jens Axboe
2010-10-14 23:30     ` Paul E. McKenney [this message]
2010-10-15  7:30       ` Jens Axboe

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