linux-kernel - Re: umount(/proc) after CLONE

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Message-ID: <20080429014718.GI5882@ZenIV.linux.org.uk>
Date:	Tue, 29 Apr 2008 02:47:18 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: umount(/proc) after CLONE_NEWNS in 2.6.25?

On Mon, Apr 28, 2008 at 07:27:59PM +0100, Al Viro wrote:
> > [pid 6308] clone(child_stack=0xbfc9de94, flags=CLONE_NEWNS|SIGCHLD) = 6309
> > [pid  6309] execve("/usr/sbin/umount", ["umount", "-n", "/proc"])
> > ...
> > [pid  6309] oldumount("/proc")          = -1 EBUSY (Device or resource busy)
> > umount: /proc: device is busy
> >
> > Yes, various NAMESPACEs are enabled (i'm trying to experiment with
> > those).
> >
> > Is it intentional?
> 
> It's very odd.  Could you bisect that down to offending changeset or
> at least narrow the things down to -rc<something>?  I'm going down right
> now, so won't be able to look into that until tonight...

Check the version of umount(8) you've got.  And see if that strace happens
to have open of /proc/mounts, without matching close by the time it calls
umount().  util-linux-ng 2.13.1 is _that_ dumb...

Please, make sure that you are using the same userland for testing - with
aforementioned version of umount(8) behaviour is triggered with .24 as well
as with .25 and there's nothing kernel could do about that...
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