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wgengine: simplify ResetAndStop, drop drain loop

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Since f343b496c3 ("wgengine, all: remove LazyWG, use wireguard-go
callback API for on-demand peers"), Reconfig is fully synchronous:
magicConn.UpdatePeers, wgdev.RemovePeer, router.Set, and dns.Set all
return when the work is done, and the peer list is updated under
wgLock before Reconfig returns. So after Reconfig with empty configs,
len(st.Peers) is already 0.

The old loop also waited for st.DERPs to drain to 0, but UpdatePeers
only edits maps; active DERP connections idle out on their own
timeout. The sole caller (LocalBackend.stopEngineAndWait) doesn't
inspect st.DERPs anyway; it just hands the Status to
setWgengineStatusLocked. So the drain-wait was for nothing observable
and could theoretically (or at least appear to readers to) loop
forever holding b.mu. Remove that reader confusion by removing
the backoff loop entirely.

Updates #19759

Change-Id: Ibfac3f0baabcad7604b713c934a8fc37932e0a50
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2026-05-14 20:54:10 +00:00 committed by Brad Fitzpatrick
parent 93440604e0
commit fa49009eee
1 changed files with 4 additions and 17 deletions
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21
wgengine/userspace.go
View File

@ -47,7 +47,6 @@ import (
"tailscale.com/types/logger"
"tailscale.com/types/netmap"
"tailscale.com/types/views"
"tailscale.com/util/backoff"
"tailscale.com/util/checkchange"
"tailscale.com/util/clientmetric"
"tailscale.com/util/eventbus"
@ -749,29 +748,17 @@ func hasOverlap(aips, rips views.Slice[netip.Prefix]) bool {
}
// ResetAndStop resets the engine to a clean state (like calling Reconfig
// with all pointers to zero values) and waits for it to be fully stopped,
// with no live peers or DERPs.
// with all pointers to zero values) and returns the resulting status.
//
// Unlike Reconfig, it does not return ErrNoChanges.
//
// If the engine stops, returns the status. NB that this status will not be sent
// to the registered status callback, it is on the caller to ensure this status
// is handled appropriately.
// The returned status will not be sent to the registered status callback;
// it is on the caller to ensure this status is handled appropriately.
func (e *userspaceEngine) ResetAndStop() (*Status, error) {
if err := e.Reconfig(&wgcfg.Config{}, &router.Config{}, &dns.Config{}); err != nil && !errors.Is(err, ErrNoChanges) {
return nil, err
}
bo := backoff.NewBackoff("UserspaceEngineResetAndStop", e.logf, 1*time.Second)
for {
st, err := e.getStatus()
if err != nil {
return nil, err
}
if len(st.Peers) == 0 && st.DERPs == 0 {
return st, nil
}
bo.BackOff(context.Background(), fmt.Errorf("waiting for engine to stop: peers=%d derps=%d", len(st.Peers), st.DERPs))
}
return e.getStatus()
}
func (e *userspaceEngine) PatchDiscoKey(pub key.NodePublic, disco key.DiscoPublic) {