fix(file): data race in tree Elem.Name#7574
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yongtang merged 1 commit intoSep 29, 2025
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #7574 +/- ##
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+ Coverage 55.70% 62.60% +6.90%
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Files 224 274 +50
Lines 10016 18329 +8313
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+ Hits 5579 11475 +5896
- Misses 3978 6187 +2209
- Partials 459 667 +208 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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Eagerly set name in newElem and make Name() read-only to avoid racy lazy writes under concurrent lookups. Add tests for empty-name comparisons and concurrent access to Less/Name(). In addition, regression tests to CloudDNS plugin. Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
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yongtang
approved these changes
Sep 29, 2025
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1. Why is this pull request needed and what does it do?
Fixes a data race in
plugin/file/treewhereElem.Name()lazily wrote the cached owner name without synchronization. Under high concurrency (e.g., clouddns lookups), this could produce torn Go strings and cause a panic ingithub.com/miekg/dns.PrevLabelwhile comparing names.The fix is to eagerly set the name in
newElem()and makeName()read-only. The cached name is set once and immutable. An alternative would be a mutex onName()but it adds lock overhead right in the hot comparator path.Also added a few tests to cover concurrent access like observed here. If the test
TestLess_ConcurrentNameAccessis run againstmasteryou'll see a data race.Details
WARNING: DATA RACE Read at 0x00c00000c338 by goroutine 11: github.com/coredns/coredns/plugin/file/tree.(*Elem).Name() /git/coredns/plugin/file/tree/elem.go:59 +0x38 github.com/coredns/coredns/plugin/file/tree.Less() /git/coredns/plugin/file/tree/elem.go:101 +0x30 github.com/coredns/coredns/plugin/file/tree.TestLess_ConcurrentNameAccess.func1() /git/coredns/plugin/file/tree/less_test.go:101 +0x74 Previous write at 0x00c00000c338 by goroutine 13: github.com/coredns/coredns/plugin/file/tree.(*Elem).Name() /git/coredns/plugin/file/tree/elem.go:63 +0x10c github.com/coredns/coredns/plugin/file/tree.Less() /git/coredns/plugin/file/tree/elem.go:101 +0x30 github.com/coredns/coredns/plugin/file/tree.TestLess_ConcurrentNameAccess.func1() /git/coredns/plugin/file/tree/less_test.go:101 +0x74 Goroutine 11 (running) created at: github.com/coredns/coredns/plugin/file/tree.TestLess_ConcurrentNameAccess() /git/coredns/plugin/file/tree/less_test.go:98 +0x204 testing.tRunner() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1934 +0x164 testing.(*T).Run.gowrap1() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1997 +0x3c Goroutine 13 (finished) created at: github.com/coredns/coredns/plugin/file/tree.TestLess_ConcurrentNameAccess() /git/coredns/plugin/file/tree/less_test.go:98 +0x204 testing.tRunner() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1934 +0x164 testing.(*T).Run.gowrap1() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1997 +0x3c ================== --- FAIL: TestLess_ConcurrentNameAccess (0.00s) testing.go:1617: race detected during execution of testAlso two additional CloudDNS tests are added:
TestCloudDNSConcurrentServeDNS: Run concurrent zone updates while concurrent queries.Details
================== WARNING: DATA RACE Write at 0x00c00061c350 by goroutine 27: github.com/coredns/coredns/plugin/file/tree.(*Elem).Name() /git/coredns/plugin/file/tree/elem.go:63 +0x10c github.com/coredns/coredns/plugin/file/tree.Less() /git/coredns/plugin/file/tree/elem.go:101 +0x30 github.com/coredns/coredns/plugin/file/tree.(*Node).search() /git/coredns/plugin/file/tree/tree.go:155 +0x54 github.com/coredns/coredns/plugin/file/tree.(*Tree).Search() /git/coredns/plugin/file/tree/tree.go:145 +0x58 github.com/coredns/coredns/plugin/file.(*Zone).Lookup() /git/coredns/plugin/file/lookup.go:96 +0x680 github.com/coredns/coredns/plugin/clouddns.(*CloudDNS).ServeDNS() /git/coredns/plugin/clouddns/clouddns.go:126 +0x464 github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentServeDNS.func2() /git/coredns/plugin/clouddns/clouddns_test.go:377 +0x2ec github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentServeDNS.gowrap1() /git/coredns/plugin/clouddns/clouddns_test.go:387 +0x40 Previous read at 0x00c00061c350 by goroutine 36: github.com/coredns/coredns/plugin/file/tree.(*Elem).Name() /git/coredns/plugin/file/tree/elem.go:64 +0x148 github.com/coredns/coredns/plugin/file/tree.Less() /git/coredns/plugin/file/tree/elem.go:101 +0x30 github.com/coredns/coredns/plugin/file/tree.(*Node).search() /git/coredns/plugin/file/tree/tree.go:155 +0x54 github.com/coredns/coredns/plugin/file/tree.(*Tree).Search() /git/coredns/plugin/file/tree/tree.go:145 +0x58 github.com/coredns/coredns/plugin/file.(*Zone).Lookup() /git/coredns/plugin/file/lookup.go:96 +0x680 github.com/coredns/coredns/plugin/clouddns.(*CloudDNS).ServeDNS() /git/coredns/plugin/clouddns/clouddns.go:126 +0x464 github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentServeDNS.func2() /git/coredns/plugin/clouddns/clouddns_test.go:377 +0x2ec github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentServeDNS.gowrap1() /git/coredns/plugin/clouddns/clouddns_test.go:387 +0x40 Goroutine 27 (running) created at: github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentServeDNS() /git/coredns/plugin/clouddns/clouddns_test.go:370 +0x5d4 testing.tRunner() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1934 +0x164 testing.(*T).Run.gowrap1() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1997 +0x3c Goroutine 36 (running) created at: github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentServeDNS() /git/coredns/plugin/clouddns/clouddns_test.go:370 +0x5d4 testing.tRunner() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1934 +0x164 testing.(*T).Run.gowrap1() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1997 +0x3c ================== --- FAIL: TestCloudDNSConcurrentServeDNS (0.04s) testing.go:1617: race detected during execution of testTestCloudDNSConcurrentLookupNameCache: Run concurrent queries and lookups, stressing the path even more.Details
================== WARNING: DATA RACE Read at 0x00c00000ec98 by goroutine 61: github.com/coredns/coredns/plugin/file/tree.(*Elem).Name() /git/coredns/plugin/file/tree/elem.go:59 +0x38 github.com/coredns/coredns/plugin/file/tree.Less() /git/coredns/plugin/file/tree/elem.go:101 +0x30 github.com/coredns/coredns/plugin/file/tree.(*Node).search() /git/coredns/plugin/file/tree/tree.go:155 +0x54 github.com/coredns/coredns/plugin/file/tree.(*Tree).Search() /git/coredns/plugin/file/tree/tree.go:145 +0x58 github.com/coredns/coredns/plugin/file.(*Zone).Lookup() /git/coredns/plugin/file/lookup.go:96 +0x680 github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentLookupNameCache.func1() /git/coredns/plugin/clouddns/clouddns_test.go:437 +0x110 github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentLookupNameCache.gowrap1() /git/coredns/plugin/clouddns/clouddns_test.go:439 +0x50 Previous write at 0x00c00000ec98 by goroutine 86: github.com/coredns/coredns/plugin/file/tree.(*Elem).Name() /git/coredns/plugin/file/tree/elem.go:63 +0x10c github.com/coredns/coredns/plugin/file/tree.Less() /git/coredns/plugin/file/tree/elem.go:101 +0x30 github.com/coredns/coredns/plugin/file/tree.(*Node).search() /git/coredns/plugin/file/tree/tree.go:155 +0x54 github.com/coredns/coredns/plugin/file/tree.(*Tree).Search() /git/coredns/plugin/file/tree/tree.go:145 +0x58 github.com/coredns/coredns/plugin/file.(*Zone).Lookup() /git/coredns/plugin/file/lookup.go:96 +0x680 github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentLookupNameCache.func1() /git/coredns/plugin/clouddns/clouddns_test.go:437 +0x110 github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentLookupNameCache.gowrap1() /git/coredns/plugin/clouddns/clouddns_test.go:439 +0x50 Goroutine 61 (running) created at: github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentLookupNameCache() /git/coredns/plugin/clouddns/clouddns_test.go:429 +0x604 testing.tRunner() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1934 +0x164 testing.(*T).Run.gowrap1() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1997 +0x3c Goroutine 86 (running) created at: github.com/coredns/coredns/plugin/clouddns.TestCloudDNSConcurrentLookupNameCache() /git/coredns/plugin/clouddns/clouddns_test.go:429 +0x604 testing.tRunner() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1934 +0x164 testing.(*T).Run.gowrap1() /opt/homebrew/Cellar/go/1.25.1/libexec/src/testing/testing.go:1997 +0x3c ================== --- FAIL: TestCloudDNSConcurrentLookupNameCache (0.05s) testing.go:1617: race detected during execution of testThese both panic on
masterbranch.2. Which issues (if any) are related?
Fixes #7561.
3. Which documentation changes (if any) need to be made?
None.
4. Does this introduce a backward incompatible change or deprecation?
No.