From mboxrd@z Thu Jan  1 00:00:00 1970
From: NeilBrown <neilb@suse.de>
Subject: Re: Bisected, with rfc/patch - was Re: BUG: unable to handle kernel
 NULL pointer dereference at sysfs_do_create_link_sd (after mdadm)
Date: Thu, 23 Apr 2015 18:03:14 +1000
Message-ID: <20150423180314.367c0876@notabene.brown>
References: <20150414171537.GH25394@azat>
	<20150423160551.45345f96@notabene.brown>
	<20150423073724.GA8139@lst.de>
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Sender: linux-raid-owner@vger.kernel.org
To: Christoph Hellwig <hch@lst.de>
Cc: Azat Khuzhin <a3at.mail@gmail.com>, "Kernel.org-Linux-RAID" <linux-raid@vger.kernel.org>, Guoqing Jiang <GQJiang@suse.com>, Tejun Heo <tj@kernel.org>, Jan Kara <jack@suse.cz>, Jens Axboe <axboe@fb.com>
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On Thu, 23 Apr 2015 09:37:24 +0200 Christoph Hellwig <hch@lst.de> wrote:

> Plase fix your device name lifetimes.

Any chance you could be more explicit?

The commit you identified doesn't seem to help much - md and dm are quite
different in this area.

It seems that it is no longer safe to call 'add_disk' between calling
'del_gendisk' and bdi_destroy being called.  How can I find out if I am in
that window, or wait for bdi_destroy to be called?

Thanks,
NeilBrown


>=20
> See the DM commit
>=20
>     63a4f0 ("dm: fix add_disk() NULL pointer due to race with free_dev()")
>=20
> for a template.
>=20
> Unregistering the device too early means we'll have half constructed
> bdis hanging around, which caused all kinds of problems for filesystems
> and the writeback code.


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