serveMap cloned s.nodes[nk], mutated the clone outside the mutex,
then wrote it back via updateNodeLocked. A concurrent UpdateNode,
SetNodeCapMap, or other writer landing between the clone and the
writeback would be silently clobbered. Mutate the live node under
the mutex instead.
Surfaces in tsnet's TestListenService as a flaky ErrUntaggedServiceHost
panic: the test calls control.UpdateNode to attach a tag, a concurrent
updateRoutine map request from the host races, and the host's next
netmap arrives with Tags=[].
Updates #19822
Change-Id: I6c5ebd5e5bf79a40316f53f627157230773cb469
Signed-off-by: James Tucker <james@tailscale.com>
James TuckerandJames Tucker
36c52ef383