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

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Message-ID: <38b2ab8a1003150509i4a9e7e1dqce2bfb11557d403d@mail.gmail.com>
Date:	Mon, 15 Mar 2010 13:09:30 +0100
From:	Francis Moreau <francis.moro@...il.com>
To:	Robert Hancock <hancockrwd@...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 Sun, Mar 14, 2010 at 5:21 PM, Robert Hancock <hancockrwd@...il.com> wrote:
> 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.
>

You're right, I don't see this anymore if I'm booting in a single user mode.

So I need to find out how to wait until these other processes stop
accessing the drive.

Thanks
-- 
Francis
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