fix: prevent SIGTERM/reload deadlock #7562
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CoreDNS could deadlock when SIGTERM arrived during an in-flight reload. Caddy’s shutdown path held the instance mutex while the reload plugin’s final-shutdown callback attempted to send on an unbuffered channel. The reload goroutine was simultaneously trying to Restart (which needed the same mutex). Changes: - Makes dnsserver.Server.Stop idempotent using sync.Once. - Reloads during shutdown are gated by checking a quit signal. Adds an integration test to validate this works properly. Signed-off-by: Ville Vesilehto <[email protected]>
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #7562 +/- ##
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+ Coverage 55.70% 62.17% +6.47%
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Files 224 274 +50
Lines 10016 18306 +8290
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+ Hits 5579 11382 +5803
- Misses 3978 6251 +2273
- Partials 459 673 +214 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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yongtang
approved these changes
Sep 19, 2025
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1. Why is this pull request needed and what does it do?
CoreDNS could deadlock when SIGTERM arrived during an in-flight reload. Caddy’s shutdown path held the instance mutex while the reload plugin’s final-shutdown callback attempted to send on an unbuffered channel. The reload goroutine was simultaneously trying to Restart (which needed the same mutex).
Changes to core:
Changes to plugin/reload:
Adds an integration test to validate this works properly.
2. Which issues (if any) are related?
Fixes #7314. Validated locally that the hang no longer happens. Depending on when the kill hits it, you might see this instead:
And then shut down.
3. Which documentation changes (if any) need to be made?
None.
4. Does this introduce a backward incompatible change or deprecation?
No.