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

Jan Kara
2015-04-21T08:59:51Z

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@suse.cz>
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR