From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752217AbdAZNSA (ORCPT <rfc822;w@1wt.eu>);
        Thu, 26 Jan 2017 08:18:00 -0500
Received: from verein.lst.de ([213.95.11.211]:48957 "EHLO newverein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751843AbdAZNR6 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 26 Jan 2017 08:17:58 -0500
Date: Thu, 26 Jan 2017 14:17:56 +0100
From: Christoph Hellwig <hch@lst.de>
To: Jan Kara <jack@suse.cz>
Cc: Dan Williams <dan.j.williams@intel.com>,
        Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>,
        Jens Axboe <axboe@kernel.dk>, Rabin Vincent <rabinv@axis.com>,
        "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-block@vger.kernel.org, Andi Kleen <andi@firstfloor.org>,
        Wei Fang <fangwei1@huawei.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [RFC PATCH v2 0/2] block: fix backing_dev_info lifetime
Message-ID: <20170126131756.GA18649@lst.de>
References: <148375097100.37020.495735345355345658.stgit@dwillia2-desk3.amr.corp.intel.com> <7780787.RVFXFXDN3H@morokweng> <CAA9_cmc5gg39kDGcWRVzBd_9VaU8rTU1ZfHWu=01n7uTNKEkRA@mail.gmail.com> <20170126100653.GB17099@quack2.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170126100653.GB17099@quack2.suse.cz>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Jan 26, 2017 at 11:06:53AM +0100, Jan Kara wrote:
> Yeah, so my patches (and I suspect your as well), have a problem when the
> backing_device_info stays around because blkdev inode still exists, device
> gets removed (e.g. USB disk gets unplugged) but blkdev inode still stays
> around (there doesn't appear to be anything that would be forcing blkdev
> inode out of cache on device removal and there cannot be because different
> processes may hold inode reference) and then some other device gets plugged
> in and reuses the same MAJOR:MINOR combination. Things get awkward there, I
> think we need to unhash blkdev inode on device removal but so far I didn't
> make this work...

The other option is to simply not release the dev_t until the backing_dev
is gone.