Re: [PATCH] blk: fix a wrong accounting of hd_struct->in_flight

Paul E. McKenney
2010-10-14T23:30:45Z

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