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

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Date:	Thu, 13 Jan 2011 11:19:21 +0900
From:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
To:	Milan Broz <mbroz@...hat.com>, Tejun Heo <tj@...nel.org>
CC:	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()

On 01/13/11 09:23, Milan Broz wrote:
> On 01/12/2011 06:34 PM, Valdis.Kletnieks@...edu wrote:
>> Seen in a boot of yesterday's linux-next.   The 'W' flag was due to the
>> already-reported 'WARNING: at kernel/workqueue.c:1202 worker_enter_idle'.
>> Not sure if it's a block_dev or dm/LVM issue, so I'm cc:'ing both groups.  I wonder
>> if the fact I still have 'CONFIG_DEVTMPFS=n' is involved (it's apparently ticking off
>> dracut before and after the warning).
>>
>> [   16.840333] dracut: Found volume group "vg_blackice" using metadata type lvm2
>> [   16.892282] dracut: The link /dev/vg_blackice/opt should had been created by udev but it was not found.  Falling back to direct link creation.
>> [   16.912627] ------------[ cut here ]------------
>> [   16.912635] WARNING: at fs/block_dev.c:824 bd_link_disk_holder+0x92/0x1ac()
> 
> That seems to be
> WARN_ON_ONCE(!bdev->bd_holder || bdev->bd_holder_disk);
> added in patch
> http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commitdiff;h=e09b457bdb7e8d23fc54dcef0930ac697d8de895
> "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.

Thanks,
-- 
Jun'ichi Nomura, NEC Corporation
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