linux-kernel - Re: [RFC PATCH v2 0/2] block: fix backing_dev

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Date:   Thu, 26 Jan 2017 14:17:56 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jan Kara <jack@...e.cz>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
        Jens Axboe <axboe@...nel.dk>, Rabin Vincent <rabinv@...s.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
        Wei Fang <fangwei1@...wei.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH v2 0/2] block: fix backing_dev_info lifetime

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.