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Date: Tue, 29 Apr 2008 03:12:28 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Michael Tokarev <mjt@tls.msk.ru>
Cc: Linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: umount(/proc) after CLONE_NEWNS in 2.6.25?
Message-ID: <20080429021228.GK5882@ZenIV.linux.org.uk>
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On Tue, Apr 29, 2008 at 03:06:38AM +0100, Al Viro wrote:

> > 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...
> 
> Umm...  Looks like something more odd is going on...

... or something much simpler:

; cat /proc/mounts |grep proc
proc /proc proc rw,nosuid,nodev,noexec 0 0
usbfs /proc/bus/usb usbfs rw 0 0
;

and unmounting the stuff mounted under /proc before doing umount /proc
works as expected.  Amazing how well the first cup of coffee helps...