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fix(healthcheck): guard periodic checks against divide-by-zero when config is cleared #3400

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fix(healthcheck): guard periodic checks against divide-by-zero when config is cleared #3400

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14 changes: 13 additions & 1 deletion internal/healthcheck/checker.go
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,8 @@ func (c *Checker) Start(ctx context.Context) (runError <-chan error, err error)
func (c *Checker) Stop() error {
c.stop()
<-c.done
c.configMutex.Lock()
defer c.configMutex.Unlock()
Comment on lines +162 to +163

@qdm12 qdm12 Jul 19, 2026

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Because above we run c.stop() to cancel the long running goroutine and wait for <-c.done, the long running goroutine should be finished and so there should be no need to hold a mutex here I think. I'll dig into this, to avoid these AI-bandaid-fixes (that do the job, but it does bloat code whereas it does not fix the real source of the problem)

@mvanhorn mvanhorn Jul 22, 2026

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You're right that after c.stop() and <-c.done the periodic goroutine can't touch these fields, so the lock in Stop isn't about that goroutine. What it guards is SetConfig: Stop runs on the collectHealthErrors goroutine (started at tunnelup.go:107, calls Stop at 148/156) while SetConfig runs on the VPN loop goroutine in onTunnelUp (tunnelup.go:88). If the loop state machine already guarantees those never overlap across a restart cycle, then the Stop hunk is redundant and I'm happy to drop it.

The part I'd keep either way is fullPeriodicCheck: on master it indexes c.tlsDialAddrs unlocked, while smallPeriodicCheck copies under the same mutex for the same fields, so this just makes the two checks consistent. The empty-slice guards also protect the try%len modulo from a divide-by-zero panic when the config is empty.

Happy to trim the PR to whichever subset you want after you've dug in.

c.tlsDialAddrs = nil
c.icmpTargetIPs = nil
c.smallCheckType = ""
Expand All @@ -170,6 +172,9 @@ func (c *Checker) smallPeriodicCheck(ctx context.Context) error {
icmpTargetIPs := make([]netip.Addr, len(c.icmpTargetIPs))
copy(icmpTargetIPs, c.icmpTargetIPs)
c.configMutex.Unlock()
if c.smallCheckType != smallCheckDNS && len(icmpTargetIPs) == 0 {
return nil
}
tryTimeouts := []time.Duration{
5 * time.Second,
5 * time.Second,
Expand Down Expand Up @@ -202,11 +207,18 @@ func (c *Checker) smallPeriodicCheck(ctx context.Context) error {
}

func (c *Checker) fullPeriodicCheck(ctx context.Context) error {
c.configMutex.Lock()
tlsDialAddrs := make([]string, len(c.tlsDialAddrs))
copy(tlsDialAddrs, c.tlsDialAddrs)
c.configMutex.Unlock()
if len(tlsDialAddrs) == 0 {
return nil
}
// 20s timeout in case the connection is under stress
// See https://github.com/qdm12/gluetun/issues/2270
tryTimeouts := []time.Duration{10 * time.Second, 15 * time.Second, 30 * time.Second}
check := func(ctx context.Context, try int) error {
tlsDialAddr := c.tlsDialAddrs[try%len(c.tlsDialAddrs)]
tlsDialAddr := tlsDialAddrs[try%len(tlsDialAddrs)]
return tcpTLSCheck(ctx, c.dialer, tlsDialAddr)
}
return withRetries(ctx, tryTimeouts, c.logger, "TCP+TLS dial", check)
Expand Down
14 changes: 14 additions & 0 deletions internal/healthcheck/checker_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,20 @@ func Test_Checker_fullcheck(t *testing.T) {
})
}

func Test_Checker_periodicCheckEmptyTargets(t *testing.T) {
t.Parallel()

checker := &Checker{smallCheckType: smallCheckICMP}

err := checker.fullPeriodicCheck(context.Background())

assert.NoError(t, err)

err = checker.smallPeriodicCheck(context.Background())

assert.NoError(t, err)
}

func Test_makeAddressToDial(t *testing.T) {
t.Parallel()

Expand Down