linux-kernel - Re: linux-next - WARNING: at fs/block_dev.c:824 bd_link_disk

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Date:	Thu, 13 Jan 2011 12:06:40 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Jun'ichi Nomura <j-nomura@...jp.nec.com>
Cc:	Milan Broz <mbroz@...hat.com>, Valdis.Kletnieks@...edu,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Neil Brown <neilb@...e.de>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-raid@...r.kernel.org,
	device-mapper development <dm-devel@...hat.com>
Subject: Re: linux-next - WARNING: at fs/block_dev.c:824
 bd_link_disk_holder+0x92/0x1ac()

Hello,

On Thu, Jan 13, 2011 at 11:19:21AM +0900, Jun'ichi Nomura wrote:
> > "block: simplify holder symlink handling"
> > 
> > dm linear just claims device in table constructor, I don't think it is bug in DM code.
> 
> The patch assumes only one holder disk for a claimed dev, which is not true.
> E.g. if there are multiple LVs on a PV.
> 
> In addition to that, since claiming is done in table constructor,
> there can be 2 claim instances for a slave/holder pair at a time
> when you load a table while there's already an active one.
> E.g. if you do lvresize.
> We need consideration for this, too.

Urgh... gees, so there actually was a user using all that cruft.
Sorry about the breakage, I'll see how multiple symlinks can be
restored.  I'm curious why this was added at all tho.  What was the
rationalization?  It's not like two subsystems can share the same
block device so marking the currently owning subsystem should have
been enough at the block layer.  There is no reason for block devices
to present information which is of no use to itself.  All that's
necessary is "this is taken by dm or md for more information, query
those".  dm and md need their own conf/representation layer anyway.

Thanks.

-- 
tejun
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