Subject: kern/2856: Mounting on directories provided by pseudo-filesystems can be lost
To: None <>
From: Wolfgang Solfrank <>
List: netbsd-bugs
Date: 10/17/1996 20:16:13
>Number:         2856
>Category:       kern
>Synopsis:       Mounting on directories provided by pseudo-filesystems can be lost
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    kern-bug-people (Kernel Bug People)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Oct 17 11:20:03 1996
NetBSD Hackers
>Release:        NetBSD-current 10/17/96
System: NetBSD august 1.2A NetBSD 1.2A (GENERIC) #23: Tue Oct 15 16:22:05 MET DST 1996
     ws@kurt:/home/NetBSD/kernel/NetBSD/sys/arch/powerpc/compile/GENERIC PowerPC

Some pseudo-filesystems provide directories.  E.g the proc filesystem has
a directory for every process in the system.  These directories can get lost
independent of any filesystem activity.  When you mount some filesystem on
such a directory, you may loose the filesystem as you can neither access any
files on it nor even do an unmount of it.

A similar problem might be in nfs, when a client does a rmdir on some
directory the server has mounted something on, or when a server does an
rmdir of a directory a client has mounted something on (albeit the latter
will at least result in some ESTALE errors), but I cannot test this at
the moment.

$ mount -t msdos /dev/ofdisk0c /proc/curproc

Subsequent mount calls will reveal a mount on /proc/xxx with xxx being some
process number, but ls /proc will not show this.