Creating concurrent snapshots / trackers of multiple block devices terminates the first one uncleanly

### Distribution Debian 12 ### Architecture amd64 ### Kernel version Linux 6.1.0-32-amd #1 SMP PREEMPT_DYNAMIC Debian 6.1.129-1 (2025-03-06) x86_64 GNU/Linux ### Blksnap version VAL-6.1 branch (6.1.2.1781) and also VAL-6.3 branch (6.3.0.73) ### Bug description When creating concurrent snapshots/trackers of different block devices, creating the second one, causes the first one to be cleaned up in a kind of unclean way. ### Steps to reproduce 1. Ordinary GPT disk with EXT4 partitions- `sda (sda1, sda2, sda3)` 2. Create tracker1 + snapshot1 for first block device - `ID=$(blksnap snapshot_create --device /dev/sda1 | grep ...)` - `blksnap stretch_snapshot --id $ID --path /.some-temp-path-snapshot1 --limit 1024 &` - `blksnap snapshot_take --id $ID` - `blksnap snapshot_collect --id $ID` # find maj:min device for the snapshot 3. Create tracker2 + snapshot2 for second block device - Same 4 commands but for e.g. /dev/sda2 5. Free snapshot2 + tracker2 for second block device - `blksnap snapshot_destroy $ID` - kill the stretch_snapshot $PID... - wait for the stretch_snapshot $PID... - `blksnap tracker_remove --device /dev/sda2` - `rm /.some-temp-path-snapshot2* || true` 7. Free snapshot1 + tracker1 for first block device - Same steps ### Expected behavior The snapshot/tracker for both devices should be safely removed. But what happens instead is: After creating the 2nd device's snapshot/tracker, - the first snapshot disappears - the first stretch_snapshot PID exits - the snapshot_collect output includes only the snapshot from the 2nd device, not the first - The first tracker cannot be removed. It is stuck in some `device busy` error. - The first block device snapshotted cannot be snapshotted again. There are these errors in dmesg: ``` Failed to copy data to diff storage with error 4 Unable to destory snapshot: cannot find snapshot by id ... Removing device [8:1] from tracking Tracker for device [8:1] is busy with a snapshot ``` ### Additional information I'm happy to provide any other wanted information,