linux-kernel - Re: why can't I remove a kernel module (or: what uses a given module)?

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Date:	Mon, 04 Dec 2006 11:39:44 +0100
From:	Tomasz Chmielewski <mangoo@...g.org>
To:	tobiasoed@...mail.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: why can't I remove a kernel module (or: what uses a given module)?

Tobias Oed wrote:
> Tomasz Chmielewski wrote:
> 
>> Ross Vandegrift wrote:
>>> On Sun, Dec 03, 2006 at 12:58:24PM +0100, Tomasz Chmielewski wrote:
>>>> You mean the "Used by" column? No, it's not used by any other module
>>>> according to lsmod output.
>>>>
>>>> Any other methods of checking what uses /dev/sda*?
>>> There's a good chance that if it was loaded at system boot, hald or
>>> udev may be doing something with it.
>> This machine doesn't have hal; when I kill udevd still doesn't help.
>>
>> Yes, something's using that drive, be it a program, a module (unlikely),
>> or something that is compiled directly in the kernel (for example,
>> md/raid1).
>> But what is it?
> 
> Since you mention md, dm comes to mind. I have seen a couple of drives that
> were previously attached to fake raid controllers becoming unavailable when
> moved to a normal controller. I haven't found the one size workaround for
> the problem yet. Can you check
> /sys/block/sda/holders ?

Yes, that was the right answer.
On a system with sata_mv (machine_1) I indeed had RAID, and that's why I 
suspected I couldn't remove the module. It was confirmed by checking 
/sys/block/sda/sda1/holders:

# ls /sys/block/sda/sda1/holders
md0@

On yet another system (machine_2), with sata_via module, I didn't set up 
RAID, but still, I couldn't remove the module. Inspecting 
/sys/block/sda/sda1/holders revealed why:

# ls /sys/block/sda/sda1/holders
dm-0@  dm-1@  dm-2@

The drive was taken from the machine_1; it had LVM2 on it.

Thanks!

-- 
Tomasz Chmielewski
http://wpkg.org

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