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nldump lister test fails when the kernel adds a neighbor mid-test #1179
Description
TestLister_ListsTheHandlesNamespace fails intermittently in the Unit Tests (root) job. On #1174, whose change touches no Go code, it failed on a re-run and passed on the next:
nldump_test.go:196: package NeighList = [{2 10 128 1 0 0 fd00:2::2 02:00:00:00:00:02 <nil> 0 0 0 0 0 0} {2 10 64 5 0 0 ff02::2 33:33:00:00:00:02 <nil> 0 0 0 6000 0 0}], %!w(<nil>); want 1 entries
--- FAIL: TestLister_ListsTheHandlesNamespace (0.00s)
The test brings a dummy link up, adds a permanent neighbor, lists neighbors once through the handle, and later lists them again through the package-level NeighList and requires the same count. Bringing the link up makes the kernel send IPv6 router solicitations in the background, which adds a NUD_NOARP entry for ff02::2 (state 64 in the output). When that entry appears between the two dumps, the second dump has two entries and the first has one.
The listing code is correct. The test compares two snapshots of state the kernel changes on its own.
Expected: the comparison ignores entries the kernel adds on its own.
Possible fixes: compare only NUD_PERMANENT entries, check that the second dump holds the test's neighbor rather than comparing counts, or turn off router solicitations on the test link (net.ipv6.conf.<link>.router_solicitations=0) before bringing it up.
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[-]TestLister_ListsTheHandlesNamespace fails when the kernel adds an ff02::2 neighbor between dumps[/-][+]nldump lister test fails when the kernel adds a neighbor mid-test[/+]privateip commentedon Oct 30, 2026
Thanks for the detailed report. This is fixed on
mainby #1177 (6715d8a), which merged shortly after this was filed. The package-levelNeighList,RuleListandRouteListchecks inTestLister_ListsTheHandlesNamespacenow check that each result holds the neighbor, rule and route the test created, instead of comparing counts against the handle's earlier dump. A kernel-addedff02::2entry can no longer fail the test.Verification on
main(72325e4), running the compiled test as root:-test.run TestLister_ListsTheHandlesNamespace -test.count=300failed 3 of 300 runs with the reportedpackage NeighList = [...]; want 1 entries, and the extra entry was theNUD_NOARPff02::2neighbor each time.main: the same run passed 300 of 300.The fix is unreleased and only on
mainso far. It touches only the test. Please reopen if you still see the flake on a run that includes 6715d8a.