Race condition when mounting loop devices
Metadata
Current evaluation
Loop partition nodes can disappear during asynchronous udev processing, intermittently breaking mounts. Although the code now waits for initial node creation, the race remains triaged and open.
Suggested action: keep open
Reason: mwhudson identified that partition devices can disappear while udevd is processing and suggested flocking the parent device through mount; a later comment reports the same failure class in #402. The current _wait_for_partition_nodes only polls for node existence, and no identified change prevents the device from disappearing before mount completion.
Evaluated by: mr-cal-bot
Impact:
56
Quick Win:
13
Complexity:
67
Confidence:
91
Actionability:
70
Issue body
### Check existing issues
- [x] I've verified that this bug isn't described by any existing issues.
### Bug description
Discovered and researched by @smethnani.
When we create loop devices, there's a race condition we sometimes hit when trying to mount them before they fully exist.
The upstream version of this bug is in https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/2045586
### Steps to reproduce
n/a it's a race condition
### Environment
We need to understand the context in which Imagecraft failed. Please let us know if you are running Imagecraft in destructive mode, whether you are using LXD or Multipass, and which operating system you are running Imagecraft on.
### imagecraft.yaml
```yaml
```
### Log output
```shell
See: https://github.com/canonical/imagecraft/actions/runs/23426535878/job/68143721209?pr=289#step:9:196
Getting partition table
Adding partition volume/pc/data3 to the image
Setting up GRUB in the image
mount: /home/imagecraft/tests/spread/pack/complex/mount: special device /dev/loop7p2 does not exist.
dmesg(1) may have more information after failed mount system call.
mount: /home/imagecraft/tests/spread/pack/complex/mount: mount failed: Unknown error 5005.
Failed to clean chroot
Detailed information: Command '['/bin/mount', '/home/imagecraft/tests/spread/pack/complex/mount', '--make-rprivate']' returned non-zero exit status 32.
Full execution log: '/root/.local/state/imagecraft/log/imagecraft-20260323-081704.190556.log'
-----
.
2026-03-23 08:17:22 Debug output for google:ubuntu-24.04-64:tests/spread/pack/complex (mar230753-821890) :
-----
++ find /root/.local/state/imagecraft/log/ -name 'imagecraft*.log'
++ sort -n
++ tail -n1
+ imagecraft_log_file=/root/.local/state/imagecraft/log/imagecraft-20260323-081704.190556.log
[...]
2026-03-23 08:17:21.218 Getting partition table
2026-03-23 08:17:21.218 Running command: ['sfdisk', '--json', 'pc.img']
2026-03-23 08:17:21.222 Adding partition volume/pc/data3 to the image
2026-03-23 08:17:21.286 Running command: ['sfdisk', '--json', 'pc.img']
2026-03-23 08:17:21.289 Setting up GRUB in the image
2026-03-23 08:17:21.289 Running command: ['losetup', '--find', '--show', '--partscan', 'pc.img']
2026-03-23 08:17:21.313 Attached image pc.img as loop device /dev/loop7
2026-03-23 08:17:21.314 [pid=57966] parent process
2026-03-23 08:17:21.314 [pid=57966] set up chroot
2026-03-23 08:17:21.314 setup chroot: PosixPath('/home/imagecraft/tests/spread/pack/complex/mount')
2026-03-23 08:17:21.314 [pid=57966] mount '/home/imagecraft/tests/spread/pack/complex/mount' on chroot
2026-03-23 08:17:21.315 mount device='/dev/loop7p2', mountpoint='/home/imagecraft/tests/spread/pack/complex/mount', args=()
2026-03-23 08:17:21.318 [pid=57966] clean up chroot
2026-03-23 08:17:21.318 cleanup chroot: PosixPath('/home/imagecraft/tests/spread/pack/complex/mount')
2026-03-23 08:17:21.318 [pid=57966] umount: '/home/imagecraft/tests/spread/pack/complex/mount'
2026-03-23 08:17:21.318 mount device='/home/imagecraft/tests/spread/pack/complex/mount', mountpoint='--make-rprivate', args=()
2026-03-23 08:17:21.321 Running command: ['losetup', '--json']
2026-03-23 08:17:21.325 Detaching loop device /dev/loop7 (from /home/imagecraft/tests/spread/pack/complex/pc.img)
2026-03-23 08:17:21.325 Running command: ['losetup', '-d', '/dev/loop7']
2026-03-23 08:17:21.327 Failed to clean chroot
2026-03-23 08:17:21.327 Detailed information: Command '['/bin/mount', '/home/imagecraft/tests/spread/pack/complex/mount', '--make-rprivate']' returned non-zero exit status 32.
2026-03-23 08:17:21.328 Full execution log: '/root/.local/state/imagecraft/log/imagecraft-20260323-081704.190556.log'
```
Evaluation history
| Date | Model | Scores | Action | Summary |
|---|---|---|---|---|
| stealth/space-bunny-alpha |
Impact:
56
Quick Win:
13
Complexity:
67
Confidence:
91
Actionability:
70
|
keep open | Loop partition nodes can disappear during asynchronous udev processing, intermittently breaking mounts. Although the code now waits for initial node creation, the race remains triaged and open. | |
| qwen/qwen3.6-35b-a3b |
Impact:
70
Quick Win:
34
Complexity:
40
Confidence:
75
Actionability:
80
|
close resolved | Race condition when mounting loop devices before partition nodes fully exist; triaged bug with maintainer confirmation. PR #428 claims to have resolved this race condition. | |
| qwen/qwen3.8-27b |
Impact:
55
Quick Win:
19
Staleness:
25
Complexity:
65
Confidence:
72
Support Request:
5
|
keep open | Race condition where loop partition devices (/dev/loopXpN) don't exist yet when mount is called after losetup --partscan. Triaged, maintainer suggested flock on parent device. Partial fix (wait for nodes) added in services/image.py via PR #428, but same failure still hit in pack path CI (19 days ago). | |
| qwen/qwen3.6-35b-a3b |
Staleness:
10
Complexity:
45
Confidence:
90
Support Request:
5
|
keep open | Intermittent race condition causes loop device partitions to disappear before mounting, leading to CI test failures. Triaged and acknowledged by maintainers, with a proposed workaround but no fix yet. | |
| qwen/qwen3.6-35b-a3b |
Staleness:
45
Complexity:
65
Confidence:
85
Support Request:
5
|
keep open | Race condition causing mount failures on loop devices due to udev processing delays. Triaged bug with maintainer suggesting flock-based synchronization. Awaiting implementation or further investigation. | |
| qwen3.6-35b-a3b-mtp-q6 |
Staleness:
45
Complexity:
45
Confidence:
90
Support Request:
5
|
keep open | Race condition causes mount failures when loop partition devices disappear before udevd finishes processing. Triaged bug with a maintainer-proposed fix, awaiting implementation. | |
| qwen3.6-35b-a3b-mtp-q6 |
Staleness:
45
Complexity:
65
Confidence:
85
Support Request:
5
|
keep open | Race condition during loop device mounting causes failures when partitions disappear before udevd finishes processing. Triaged, with a maintainer suggesting flock-based synchronization. |
Update history
| Date | Change |
|---|---|
| updated |
Related work
-
Related To:
canonical/imagecraft#402
(confidence 95%)
A later issue comment reports the same class of loop-device mount failure during this PR's test run.
-
Related To:
canonical/imagecraft#428
(confidence 82%)
This change introduced the current partition-node wait, but it does not hold a parent-device lock through the mount.
Related issues
No related issues found above the similarity threshold.