linux-kernel - sys_umount() returns EBUSY when doing: sh -c "mount /dev/sdc1 /mnt; umount /mnt"

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Date:	Sat, 13 Mar 2010 09:56:25 +0100
From:	Francis Moreau <francis.moro@...il.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: sys_umount() returns EBUSY when doing: sh -c "mount /dev/sdc1 /mnt; 
	umount /mnt"

Hello

I've some shell scripts which try to find out the filesystem hosted by
a block device.

They basically do this:

    mount /dev/sdc1 /mnt
    fs=$(stat -f -c %T $mount_point)
    umount /mnt

It happens to work but since an unknown upgrade (kernel, libs or tools
upgrade), umount(8) returns -EBUSY.

I found that it's actually the sys_umount() which return -EBUSY.

So the question, is this expected or is this a regression ?

If it's expected then which operation should I add between the
mount(8) and umount(8) to make the mount operation completely finish
(inside the kernel) so the next umount won't return -EBUSY ?

Oh I'm currently using the kernel shipped with F12: 2.6.32.9-67.fc12.x86_64

Thanks
-- 
Francis
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