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

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Date:	Sun, 14 Mar 2010 10:21:50 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Francis Moreau <francis.moro@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: sys_umount() returns EBUSY when doing: sh -c "mount /dev/sdc1
 /mnt;  umount /mnt"

On 03/13/2010 02:56 AM, Francis Moreau wrote:
> 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 ?

If no other process were involved I would say it's likely a bug. 
However, my guess is that some other process (HAL, something in GNOME, 
etc.) detects the mount and decides to start accessing the drive. Then 
when you immediately try to unmount, it fails because it's busy. I 
suspect if you try this in single-user mode with no unnecessary 
processes running you won't see this.

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

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