Avoid concurrent write corruption to /etc/hosts #6893
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* Add a mutex around /etc/hosts updates (for a little extra safety) * Don't write unchanged files * Recover from out-of-sequence guard lines * Add tests Thanks to granular-ryanbonham for the suggestions & finding the issue!
When we have multiple writers racing to write /etc/hosts, we could have file corruption where we see a mix of both files. We can't use a traditional atomic file write, because we are bind-mounting /etc/hosts. Instead we write to /etc/hosts, pause, then re-read the contents. If the contents don't match, we repeat. This will not result in fair queuing, but will avoid corruption.
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This seems like a good solution/work around for me. Thanks @justinsb!
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: justinsb, mikesplain The full list of commands accepted by this bot can be found here. The pull request process is described here
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Not sure how I removed the lgtm but... Thanks @justinsb! |
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…ck-of-#6893-upstream-release-1.12 Cherry pick of #6893 upstream release 1.12
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When we have multiple writers racing to write /etc/hosts, we could
have file corruption where we see a mix of both files.
We can't use a traditional atomic file write, because we are
bind-mounting /etc/hosts.
Instead we write to /etc/hosts, pause, then re-read the contents. If
the contents don't match, we repeat. This will not result in fair
queuing, but will avoid corruption.