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ipn/ipnserver: fix TestConcurrentOSUserSwitchingOnWindows

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I made a last-minute change in #14626 to split a single loop that created 1_000 concurrent
connections into an inner and outer loop that create 100 concurrent connections 10 times.
This introduced a race because the last user's connection may still be active (from the server's
perspective) when a new outer iteration begins. Since every new client gets a unique ClientID,
but we reuse usernames and UIDs, the server may let a user in (as the UID matches, which is fine),
but the test might then fail due to a ClientID mismatch:
server_test.go:232: CurrentUser(Initial): got &{S-1-5-21-1-0-0-1001 User-4 <nil> Client-2 false false};
want &{S-1-5-21-1-0-0-1001 User-4 <nil> Client-114 false false}

In this PR, we update (*testIPNServer).blockWhileInUse to check whether the server is currently busy
and wait until it frees up. We then call blockWhileInUse at the end of each outer iteration so that the server
is always in a known idle state at the beginning of the inner loop. We also check that the current user
is not set when the server is idle.

Updates tailscale/corp#25804
Updates #14655 (found when working on it)

Signed-off-by: Nick Khyl <nickk@tailscale.com>
This commit is contained in:
Nick Khyl 2025-01-15 14:22:14 -06:00 committed by Nick Khyl
parent d8b00e39ef
commit 62fb857857
1 changed files with 14 additions and 1 deletions
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15
ipn/ipnserver/server_test.go
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@ -251,6 +251,12 @@ func TestConcurrentOSUserSwitchingOnWindows(t *testing.T) {
}()
}
wg.Wait()
if err := server.blockWhileInUse(ctx); err != nil {
t.Fatalf("blockWhileInUse: %v", err)
}
server.checkCurrentUser(nil)
}
}
@ -346,7 +352,14 @@ func (s *testIPNServer) makeTestUser(name string, clientID string) *ipnauth.Test
func (s *testIPNServer) blockWhileInUse(ctx context.Context) error {
ready, cleanup := s.zeroReqWaiter.add(&s.mu, ctx)
<-ready
s.mu.Lock()
busy := len(s.activeReqs) != 0
s.mu.Unlock()
if busy {
<-ready
}
cleanup()
return ctx.Err()
}