Ya happens as stated by Yoshino: This problem occurs especially when
proc filesystem is mounted inside a chrooted environment; affecting
pbuilder/cowbuilder.
When you mount proc in a mountpoint via chroot, the /etv/mtab entry
doesn't contains the newly mounted proc (as debootstrap do, for example).
# chroot /var/cache/pbuilder/build/1631 mount -t proc proc /proc
# cat /etc/fstab
proc /proc proc nodev,noexec,nosuid 0 0
.
.
.
(the /etc/mtab entry doesn't contains newly mounted proc, only the
system one is present)
now, if i try to umount /var/cache/pbuilder/build/1631/proc when my cwd
is /var/cache/pbuilder/build/1631 it fails:
root@pr0gg3d:/var/cache/pbuilder/build/1631# umount -vv
/var/cache/pbuilder/build/1631/proc
Trying to unmount /var/cache/pbuilder/build/1631/proc
umount: /proc: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
Notice *how it tries to umount /proc*. But if i change my working dir,
it works:
root@pr0gg3d:/var/cache/pbuilder/build/1631# cd ..
root@pr0gg3d:/var/cache/pbuilder/build# umount -vv
/var/cache/pbuilder/build/1631/proc
Trying to unmount /var/cache/pbuilder/build/1631/proc
Could not find /var/cache/pbuilder/build/1631/proc in mtab
/var/cache/pbuilder/build/1631/proc has been unmounted
root@pr0gg3d:/var/cache/pbuilder/build#
Imho this problem was introduced from the 2.19.1-rc1. The commit is
http://anonscm.debian.org/gitweb/?p=users/lamont/util-linux.git;a=commitdiff;h=06b814cc5c7cfcf6f4284aa1a0d140f322e66594;hp=f7e08f83faae3def36423bee75638f7e69f495a2
Introducing the canonicalization of fsname(s) in getmntdevbackward(),
the standard proc entry it's seen as non-canonical name and
canonicalize() tries to match with the cwd path.
If there's a match (/var/cache/pbuilder/build/1631/proc) it tries to
umount the associated mountpoint /proc but this is wrong.
Changing the working path, as in my example above, the
/var/cache/pbuilder/build/proc doesn't exists, and the code assumes that
there's no match in /etc/mtab, prints "Could not find
/var/cache/pbuilder/build/1631/proc in mtab" and tries to unmount the
passed mountpoint.
It sounds like a bug for me. Consider that we have this behaviour also
for the others spec as "none" "sysfs" and so on...
Maybe we should use the canonicalize_spec() in getmntdevbackward()
instead of a plain canonicalize(), because proc (and others) shouldn't
considered as a non-canonical-path but as a spec one (as
canonicalize_spec() does).
Here is a patch against git
diff --git a/mount/fstab.c b/mount/fstab.c
index 8ce733b..32cf467 100644
--- a/mount/fstab.c
+++ b/mount/fstab.c
@@ -314,9 +314,11 @@ getmntdevbackward (const char *name, struct
mntentchn *mcprev) {
return mc;
}
- /* non-canonical names in mtab (this is BAD THING!) */
+ /* non-canonical names in mtab (this is BAD THING!)
+ * but it should be allowed only for spec fsname(s)
+ */
for (mc = mcprev->prev; mc && mc != mc0; mc = mc->prev) {
- char *cn = canonicalize(mc->m.mnt_fsname);
+ char *cn = canonicalize_spec(mc->m.mnt_fsname);
int res = cn ? streq(cn, name) : 0;
free(cn);
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