linux-kernel - Re: [PATCH 03/12] writeback: move dirty inodes from super_block to backing_dev

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Message-ID: <20090525085104.GO11363@kernel.dk>
Date:	Mon, 25 May 2009 10:51:04 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	chris.mason@...cle.com, david@...morbit.com, hch@...radead.org,
	akpm@...ux-foundation.org, yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH 03/12] writeback: move dirty inodes from super_block to
	backing_dev_info

On Mon, May 25 2009, Jan Kara wrote:
> On Mon 25-05-09 09:34:38, Jens Axboe wrote:
> > This is a first step at introducing per-bdi flusher threads. We should
> > have no change in behaviour, although sb_has_dirty_inodes() is now
> > ridiculously expensive, as there's no easy way to answer that question.
> > Not a huge problem, since it'll be deleted in subsequent patches.
> > 
> > Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> > ---
> >  fs/fs-writeback.c           |  196 +++++++++++++++++++++++++++---------------
> >  fs/super.c                  |    3 -
> >  include/linux/backing-dev.h |    9 ++
> >  include/linux/fs.h          |    5 +-
> >  mm/backing-dev.c            |   30 +++++++
> >  mm/page-writeback.c         |   11 +--
> >  6 files changed, 170 insertions(+), 84 deletions(-)
> ...
> > @@ -225,9 +231,23 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
> >  }
> >  EXPORT_SYMBOL(bdi_register_dev);
> >  
> > +static void bdi_remove_from_list(struct backing_dev_info *bdi)
> > +{
> > +	mutex_lock(&bdi_lock);
> > +	list_del_rcu(&bdi->bdi_list);
> > +	mutex_unlock(&bdi_lock);
> > +
> > +	/*
> > +	 * In case the bdi is freed right after unregister, we need to
> > +	 * make sure any RCU sections have exited
> > +	 */
> > +	synchronize_rcu();
> > +}
> > +
>   Is this RCU thing still valid? And in bdi_register_dev() as well...

Not it isn't, apparently that bit didn't get killed from the intermedia
steps. The final version doesn't contain any RCU for
bdi_list/bdi_pending_list. I'll shuffle this back as well, thanks for
noticing!

-- 
Jens Axboe

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