Fix race on state serialization

Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com>

daemon/state.go

@@ -1,6 +1,7 @@
 package daemon
 
 import (
+	"encoding/json"
 	"fmt"
 	"sync"
 	"time"
@@ -49,6 +50,16 @@ func (s *State) String() string {
 	return fmt.Sprintf("Exited (%d) %s ago", s.ExitCode, units.HumanDuration(time.Now().UTC().Sub(s.FinishedAt)))
 }
 
+type jState State
+
+// MarshalJSON for state is needed to avoid race conditions on inspect
+func (s *State) MarshalJSON() ([]byte, error) {
+	s.RLock()
+	b, err := json.Marshal(jState(*s))
+	s.RUnlock()
+	return b, err
+}
+
 func wait(waitChan <-chan struct{}, timeout time.Duration) error {
 	if timeout < 0 {
 		<-waitChan