Bug#1143737: gnome-system-monitor: Root partition usage inflated by separate LUKS/dm-crypt ext4 mounts under /mnt

[harold]

Package: gnome-system-monitor
Version: 48.1-2
Severity: normal
X-Debbugs-Cc: harold88832 at outlook.com

Dear Maintainer,

GNOME System Monitor (gnome-system-monitor) shows “Root partition” used space inflated when additional ext4 filesystems are mounted under /mnt and are backed by LUKS/dm-crypt (device-mapper) volumes. The inflated UI values do not match authoritative filesystem usage reported by `df`.

Environment:
- OS: Debian 13 (amd64), GNOME desktop
- Kernel: 6.12.96+deb13-amd64
- gnome-system-monitor: 48.1-2 (stable)

Storage layout (relevant):
- `/` is ext4 on `/dev/mapper/debian--13--vg-root` (via LUKS → LVM)
- `/mnt/data1` and `/mnt/data2` are separate ext4 mounts, each on a distinct `/dev/mapper/luks-*` (via LUKS → dm-crypt)

Steps to reproduce:
1. Ensure `/` is mounted on LUKS+LVM ext4 (root).
2. Ensure two separate LUKS-backed ext4 filesystems are mounted under `/mnt/data1` and `/mnt/data2`.
3. Open GNOME System Monitor.
4. Increase used space on either/both `/mnt/data1` and `/mnt/data2`.
5. Observe the “Root partition” used value.

Expected:
- “Root partition” usage should reflect only the filesystem mounted at `/`.
- Used space on `/mnt/data1` and `/mnt/data2` should not be attributed to `/`.

Actual:
- “Root partition” used space increases as if it includes used space from `/mnt/data1` and/or `/mnt/data2`.

Authoritative filesystem usage evidence:
- `df -h /`:
  /dev/mapper/debian--13--vg-root  448G  213G  213G  50% /
- `df -h /mnt/data1/`:
  /dev/mapper/luks-*  458G   47G  388G  11% /mnt/data1
- `df -h /mnt/data2/`:
  /dev/mapper/luks-*  458G  110G  325G  26% /mnt/data2

Mount-to-device mapping evidence:
- `findmnt -R / -o TARGET,SOURCE,FSTYPE | grep '^├─/mnt'`:
  - /mnt/data1 -> /dev/mapper/luks-* (ext4)
  - /mnt/data2 -> /dev/mapper/luks-* (ext4)

Additional context:
- In a Debian 13 GNOME VM where `/mnt/data` is just a plain virtual disk (no LUKS/dm-crypt/LVM layering), GNOME System Monitor reports root and the extra mount separately as expected.

Would be happy to provide logs/screenshots if needed.

Thanks,
harold


-- System Information:
Debian Release: 13.6
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.12.96+deb13-amd64 (SMP w/8 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages gnome-system-monitor depends on:
ii  dconf-gsettings-backend [gsettings-backend]  0.40.0-5
ii  libadwaita-1-0                               1.7.6-1~deb13u1
ii  libc6                                        2.41-12+deb13u3
ii  libcairo2                                    1.18.4-1+b1
ii  libgcc-s1                                    14.2.0-19
ii  libgdk-pixbuf-2.0-0                          2.42.12+dfsg-4+deb13u1
ii  libglib2.0-0t64                              2.84.4-3~deb13u3
ii  libglibmm-2.68-1t64                          2.84.0-1
ii  libgraphene-1.0-0                            1.10.8-5
ii  libgtk-4-1                                   4.18.6+ds-2
ii  libgtkmm-4.0-0                               4.18.0-1
ii  libgtop-2.0-11                               2.41.3-1+b2
ii  libpango-1.0-0                               1.56.3-1
ii  libpangocairo-1.0-0                          1.56.3-1
ii  librsvg2-2                                   2.60.0+dfsg-1
ii  libsigc++-3.0-0                              3.6.0-2+b1
ii  libstdc++6                                   14.2.0-19
ii  libsystemd0                                  257.13-1~deb13u1

Versions of packages gnome-system-monitor recommends:
ii  gvfs  1.57.2-2+deb13u1

Versions of packages gnome-system-monitor suggests:
ii  pkexec  126-2

-- no debconf information