From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Petazzoni Date: Tue, 10 Mar 2015 18:59:37 +0100 Subject: [Buildroot] Obscure bug in Util-Linux umount? In-Reply-To: <54FF18D4.2030709@ou.edu> References: <54FE7E8E.20306@ou.edu> <54FF18D4.2030709@ou.edu> Message-ID: <20150310185937.280f8497@free-electrons.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net Dear Steve Kenton, On Tue, 10 Mar 2015 11:16:20 -0500, Steve Kenton wrote: > Further testing revealed that it only occurs if the embedded root filesystem is read-only > which I forgot to mention (blush) so it's probably an interaction with a stale /etc/mtab > or something, but only for the root filesystem and only if the mount point directory names > are the same, yada etc. Much less likely to bite anyone else so I guess a heads up is not needed. > > Any way, not really a bug but rather a feature with undefined behaviour and most importantly > a case of 'it hurts if I do this' soooo 'don't do that'! Interesting. After reading your e-mail, I had a very quick look at the kernel side and util-linux side, looking for code using the s_last_mounted field of the superblock which indeed contains the last location where it was mounted. But I couldn't spot any place where it is specifically used to prevent something from happening. But I didn't spend a lot of time, so I may very well have missed something. Thomas -- Thomas Petazzoni, CTO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com