[arch-releng] [PATCH 1/1] explicitly detach loop device on umount

Tue Apr 21 22:43:12 UTC 2015

Gerardo Exequiel Pozzi <vmlinuz386 at gmail.com> on Tue, 2015/04/21 19:23:
> On 04/21/2015 02:57 AM, Christian Hesse wrote:
> > From: Christian Hesse <mail at eworm.de>
> > 
> > I see cases where a stale loop device stays around and fills up my
> > partition as image file is still in use and does not get unlinked.
> > 
> > Explicitly detach loop device on umount to fix that.
> > 
> > Signed-off-by: Christian Hesse <mail at eworm.de>
> > ---
> >  archiso/mkarchiso       | 2 +-
> >  configs/releng/build.sh | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/archiso/mkarchiso b/archiso/mkarchiso
> > index 0da02b0..bc82786 100755
> > --- a/archiso/mkarchiso
> > +++ b/archiso/mkarchiso
> > @@ -59,7 +59,7 @@ _mount_airootfs() {
> >  
> >  _umount_airootfs() {
> >      _msg_info "Unmounting '${work_dir}/mnt/airootfs'"
> > -    umount "${work_dir}/mnt/airootfs"
> > +    umount -d "${work_dir}/mnt/airootfs"
> >      _msg_info "Done!"
> >      rmdir "${work_dir}/mnt/airootfs"
> >      trap - EXIT HUP INT TERM
> > diff --git a/configs/releng/build.sh b/configs/releng/build.sh
> > index 5590163..86cdb08 100755
> > --- a/configs/releng/build.sh
> > +++ b/configs/releng/build.sh
> > @@ -190,7 +190,7 @@ make_efiboot() {
> >      cp ${work_dir}/iso/EFI/shellx64_v2.efi ${work_dir}/efiboot/EFI/
> >      cp ${work_dir}/iso/EFI/shellx64_v1.efi ${work_dir}/efiboot/EFI/
> >  
> > -    umount ${work_dir}/efiboot
> > +    umount -d ${work_dir}/efiboot
> >  }
> >  
> >  # Build airootfs filesystem image
> > 
> 
> Hi Chris,

Hi Gerardo, hi Pierre,

(Pierre, CCing you as you build the official media.)

> Weird, I never experienced such thing, maybe some kind of race
> condition. I guess should be reported to upstream.

I had some problems with systemd 219... It 'magically' umounts loop mounts,
which breaks archiso.

# truncate -s 1G /tmp/test.img
# mkfs.ext4 /tmp/test.img
[...]
# mount -o loop /tmp/test.img /mnt/tmp

systemd umounts the image as it thinks it is inactive:

Apr 20 08:54:28 leda systemd[1]: Unit mnt-tmp.mount is bound to inactive
unit. Stopping, too.
Apr 20 08:54:28 leda systemd[1]: Unmounting /mnt/tmp...
Apr 20 08:54:28 leda systemd[1]: Unmounted /mnt/tmp.

However manually assigning a loop device and mounting that works just fine in
most cases. (However I saw a user instance of systemd doing similar things...
So it still broke from time to time.)

# losetup -f /tmp/test.img
# losetup -a
/dev/loop0: [0034]:695793 (/tmp/test.img)
# mount /dev/loop0 /mnt/tmp

I applied these upstream patches to systemd 219-5 to fix the problem and get
better information on further problems:

--- start first patch ----
From 628c89cc68ab96fce2de7ebba5933725d147aecc Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart at poettering.net>
Date: Fri, 27 Feb 2015 21:55:08 +0100
Subject: core: rework device state logic

This change introduces a new state "tentative" for device units. Device
units are considered "plugged" when udev announced them, "dead" when
they are not available in the kernel, and "tentative" when they are
referenced in /proc/self/mountinfo or /proc/swaps but not (yet)
announced via udev.

This should fix a race when device nodes (like loop devices) are created
and immediately mounted. Previously, systemd might end up seeing the
mount unit before the device, and would thus pull down the mount because
its BindTo dependency on the device would not be fulfilled.

--- start second patch ----
From 98f738b62047229af4a929d7996e2ab04253b02c Mon Sep 17 00:00:00 2001
From: Colin Walters <walters at verbum.org>
Date: Tue, 17 Feb 2015 13:47:34 -0500
Subject: unit: When stopping due to BindsTo=, log which unit caused it

I'm trying to track down a relatively recent change in systemd
which broke OSTree; see https://bugzilla.gnome.org/show_bug.cgi?id=743891

Systemd started to stop sysroot.mount, and this patch should help
me debug why at least.

While we're here, "break" on the first unit we find that will
deactivate, as there's no point in further iteration.

--- start third patch ----
From 5bd4b173605142c7be493aa4d958ebaef21f421d Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart at poettering.net>
Date: Wed, 25 Feb 2015 22:05:14 +0100
Subject: unit: use weaker dependencies between mount and device units in
 --user mode

When running in user mode unmounting of mount units when a device
vanishes is unlikely to work, and even if it would work is already done
by PID 1 anyway. HEnce, when creating implicit dependencies between
mount units and their backing devices, created a Wants= type dependency
in --user mode, but leave a BindsTo= dependency in --system mode.
--- end patches ---

I can work with loop device just fine now. However loop devices are no longer
detached automatically. Not sure if systemd caused this or any other change
happened.

> Anyway I will push the patch, thank you.

Thanks!
-- 
main(a){char*c=/*    Schoene Gruesse                         */"B?IJj;MEH"
"CX:;",b;for(a/*    Chris           get my mail address:    */=0;b=c[a++];)
putchar(b-1/(/*               gcc -o sig sig.c && ./sig    */b/42*2-3)*42);}
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