From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755501AbbDTSRS (ORCPT ); Mon, 20 Apr 2015 14:17:18 -0400 Received: from mail-qg0-f50.google.com ([209.85.192.50]:34798 "EHLO mail-qg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754571AbbDTSRN (ORCPT ); Mon, 20 Apr 2015 14:17:13 -0400 Date: Mon, 20 Apr 2015 14:17:07 -0400 From: Tejun Heo To: Jan Kara Cc: axboe@kernel.dk, linux-kernel@vger.kernel.org, hch@infradead.org, hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org, vgoyal@redhat.com, lizefan@huawei.com, cgroups@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.cz, clm@fb.com, fengguang.wu@intel.com, david@fromorbit.com, gthelen@google.com Subject: Re: [PATCH 15/49] writeback: move backing_dev_info->wb_lock and ->worklist into bdi_writeback Message-ID: <20150420181707.GD4206@htj.duckdns.org> References: <1428350318-8215-1-git-send-email-tj@kernel.org> <1428350318-8215-16-git-send-email-tj@kernel.org> <20150420153224.GD17020@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150420153224.GD17020@quack.suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > 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. Thanks. -- tejun