linux-kernel - Re: [PATCH 15/49] writeback: move backing_dev_info->wb_lock and ->worklist into bdi

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Date:	Tue, 21 Apr 2015 10:59:42 +0200
From:	Jan Kara <jack@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jan Kara <jack@...e.cz>, axboe@...nel.dk,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	hannes@...xchg.org, linux-fsdevel@...r.kernel.org,
	vgoyal@...hat.com, lizefan@...wei.com, cgroups@...r.kernel.org,
	linux-mm@...ck.org, mhocko@...e.cz, clm@...com,
	fengguang.wu@...el.com, david@...morbit.com, gthelen@...gle.com
Subject: Re: [PATCH 15/49] writeback: move backing_dev_info->wb_lock and
 ->worklist into bdi_writeback

On Mon 20-04-15 14:17:07, Tejun Heo wrote:
> Hello, Jan.
> 
> On Mon, Apr 20, 2015 at 05:32:24PM +0200, Jan Kara wrote:
> > > @@ -454,9 +451,9 @@ EXPORT_SYMBOL(bdi_init);
> > >  
> > >  void bdi_destroy(struct backing_dev_info *bdi)
> > >  {
> > > -	bdi_wb_shutdown(bdi);
> > > -
> > > -	WARN_ON(!list_empty(&bdi->work_list));
> > > +	/* make sure nobody finds us on the bdi_list anymore */
> > > +	bdi_remove_from_list(bdi);
> > > +	wb_shutdown(&bdi->wb);
> > >  
> > >  	if (bdi->dev) {
> > >  		bdi_debug_unregister(bdi);
> >   But if someone ends up calling bdi_destroy() on unregistered bdi,
> > bdi_remove_from_list() will be corrupting memory, won't it? And if I
> 
> bdi_init() does INIT_LIST_HEAD() on it, so it should be fine, no?
  Yeah, checking the code again, we are fine.

> > remember right there were some corner cases where this really happened.
> > Previously we were careful and checked WB_registered. I guess we could
> > check for !list_empty(&bdi->bdi_list) and also reinit bdi_list in
> > bdi_remove_from_list() after synchronize_rcu_expedited().
> 
> But we can't call bdi_destroy() more than once no matter what.  We'd
> be doing double frees.
  Sorry, I was thinking about calling bdi_unregister() more than once but
as the call is moved into bdi_destroy() that is really called only once.

You can add:
Reviewed-by: Jan Kara <jack@...e.cz>
								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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