Yu Watanabe
c21a49cd3d
Fixes #43442. A `.swap` unit can end up **active but unloadable, with no device**, and stopping such a unit aborts PID 1. ### What it looks like ``` $ systemctl show 'dev-disk-byx2dpartlabel-primary.swap' -p LoadState,ActiveState,What LoadState=not-found ActiveState=active What= # <-- no device $ systemctl stop 'dev-disk-byx2dpartlabel-primary.swap' systemd[1]: About to execute: /usr/sbin/swapoff # <-- no argument systemd[1]: Caught <ABRT>, from our own process. systemd[1]: Freezing execution. ``` PID 1 stays alive but frozen, so the machine stops answering `systemctl` and never reboots. ### How it happens 1. systemd creates one `.swap` unit per udev device link of every device in `/proc/swaps`. 2. A device link gets repointed at another device while the swap stays on. `/proc/swaps` doesn't change, so nothing re-examines the unit — it stays active. 3. The next `daemon-reload` drops all units and rebuilds them. Enumeration from `/proc/swaps` no longer produces this name, so only the deserialization brings the unit back: by name, with no fragment on disk. 4. `swap_load()` only calls `swap_add_extras()` for units that loaded a fragment or are backed by `/proc/swaps`, so this one gets neither a `What=` nor a patched `ExecContext`. 5. `swap_coldplug()` restores its active state anyway. 6. Shutdown stops it. `unit_stop()` deliberately permits stopping units whose load failed, so it reaches `exec_spawn()` and trips the `PrivateVarTmp=` assertion in `exec_context_serialize()`.
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