linux-kernel - Re: [PATCH] blk: fix a wrong accounting of hd_struct->in

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Message-ID: <4CB6FB30.1000502@kernel.dk>
Date:	Thu, 14 Oct 2010 14:44:32 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk: fix a wrong accounting of hd_struct->in_flight

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.

-- 
Jens Axboe

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