linux-kernel - /proc/mounts vs mount inconsistency in 2.6.16 (SLES10 SP1)

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Message-ID: <4808B4B2.23552.144FC9C0@Ulrich.Windl.rkdvmks1.ngate.uni-regensburg.de>
Date:	Fri, 18 Apr 2008 14:48:27 +0200
From:	"Ulrich Windl" <ulrich.windl@...uni-regensburg.de>
To:	linux-kernel@...r.kernel.org
Subject: /proc/mounts vs mount inconsistency in 2.6.16 (SLES10 SP1)

Hi,

I think I found a little problem in kernel 2.6.16.54-0.2.5-xen (Current SLES10 
SP1):

By mistake I mounted some filesystem read-only over /.

Realizing the mistake, I did an "umount /", which seemed to work.

Then I noticed that / was mounted read-only, while the files being there were 
those of the right root filesystem.

So I did a "Mount  -o remount /" which enabled writes again.

As some other program had odd effects, I did "cat /proc/mounts" which still 
displayed the wrong device and readonly (/dev/system/as2-root / reiserfs ro 0 0), 
while umount refused to unmount it "umount: /dev/system/as2-root: not mounted".

It seems the interface between the mount/umount program and /proc/mounts is a bit 
instable...

Some Details:
Device /dev/system/as2-root is mounted in the privileged domain,
and so cannot be mounted by a guest.
 # mount
/dev/mapper/system-root on / type reiserfs (rw)
[...]
# cat /proc/mounts
rootfs / rootfs rw 0 0
[...]
/dev/system/as2-root / reiserfs ro 0 0
# umount /dev/system/as2-root
umount: /dev/system/as2-root: not mounted
# umount -f /dev/system/as2-root
umount2: Invalid argument
umount: /dev/system/as2-root: not mounted
# mount -o remount /dev/system/root / ### having looked it up in /etc/fstab
# cat /proc/mounts
rootfs / rootfs rw 0 0
[...]
/dev/system/as2-root / reiserfs ro 0 0
# mount /dev/system/root /
# cat /proc/mounts
rootfs / rootfs rw 0 0
[...]
/dev/system/as2-root / reiserfs ro 0 0
# umount / ### succeeds!
# mount /dev/system/root /
mount: /dev/system/root already mounted or / busy
mount: according to mtab, /dev/mapper/system-root is already mounted on /
# cat /proc/mounts
rootfs / rootfs rw 0 0
[...]
/dev/system/as2-root / reiserfs ro 0 0
/dev/system/root / reiserfs ro 0 0
# xm create -c as2
Using config file "/etc/xen/vm/as2".
Error: Device 2049 (vbd) could not be connected.
Device /dev/system/as2-root is mounted in the privileged domain,
and so cannot be mounted by a guest.

S**t: Isn't there a solution other than rebooting Dom0 (XEN talk)?

Regards,
Ulrich
P.S. I'm not subscribed to the kernel list, so if you want to reach me, please CC:

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