fix: handle busy cgroup mounts on Bottlerocket - #181
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Bottlerocket can retain references to the inherited cgroup2 mount, causing the normal unmount to fail with EBnUSY and preventing dockerd from starting. Fall back to a lazy detach before installing the correctly rooted mount. If both unmount attempts fail, retain the inherited mount and continue with potentially degraded cgroup attribution rather than failing the workspace. Refs: https://linear.app/codercom/issue/PLAT-637
geokat
marked this pull request as ready for review
September 14, 2026 23:07
BobbyHo
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Sep 14, 2026
Only configure /init delegation after confirming that the cgroup mount is rooted at / in the new cgroup namespace. If neither unmount method can detach the inherited mount, or the replacement mount remains incorrectly rooted, start dockerd without nesting setup and warn that inner container cgroup attribution may be incorrect.
BobbyHo
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Sep 15, 2026
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lgtm. Thank you for addressing my comments.
Starting dockerd in the new cgroup namespace with the inherited mount leaves the namespace and mount roots misaligned, causing the runtime to look for workspace cgroups at paths that do not exist. If neither unmount method can detach the inherited mount, re-enter the parent cgroup namespace before starting dockerd. This preserves workspace functionality while accepting potentially incorrect inner cgroup attribution. Fail explicitly if a replacement mount remains incorrectly rooted, since the original mount has already been detached.
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Testing the fallback path on EKS showed that skipping the /init and subtree-control setup was not enough to restore functionality. |
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On Bottlerocket, runtime-held references to the inherited cgroup2 mount
can cause the normal unmount to fail with EBUSY, preventing dockerd
from starting.
Fall back to a lazy detach before installing the correctly rooted
mount. If neither unmount method can detach the inherited mount,
re-enter the parent cgroup namespace before starting dockerd. This
preserves workspace functionality with 0.6.7-like cgroup attribution.
Refs:
https://linear.app/codercom/issue/PLAT-637