enable logging in http server + fix race condition between 2 executors goroutines calling MaxSignal() simultaneously from the RPC server's connection loops

Author: matankalina

syz-verifier/main.go

@@ -113,6 +113,7 @@ func main() {
 	}
 	osutil.MkdirAll(workdir)
 
+	log.EnableLogCaching(1000, 1<<20)
 	log.Logf(0, "initialized %d sources", len(sources))
 
 	vrf := &Verifier{

syz-verifier/verifier.go

@@ -689,17 +689,32 @@ func (kernel *Kernel) CoverageFilter(modules []*vminfo.KernelModule) ([]uint64,
 }
 
 func (kernel *Kernel) MaxSignal() signal.Signal {
-	if kernel.phase >= kPhaseLoadedQueue {
-		kernel.reqMaxSignal <- kernel.id
-		kernel.setPhaseLocked(kPhaseAwaitingMaxSignal)
-		sig := <-kernel.maxSignal
-		kernel.setPhaseLocked(kPhaseLoadedQueue)
-		return sig
+	kernel.mu.Lock()
+	if kernel.phase < kPhaseLoadedQueue {
+		kernel.mu.Unlock()
+		return nil
 	}
-	return nil
+	if kernel.phase == kPhaseAwaitingMaxSignal {
+		// Another goroutine is already requesting max signal
+		kernel.mu.Unlock()
+		return nil
+	}
+	kernel.phase = kPhaseAwaitingMaxSignal
+	kernel.mu.Unlock()
+
+	kernel.reqMaxSignal <- kernel.id
+	sig := <-kernel.maxSignal
+
+	kernel.mu.Lock()
+	kernel.phase = kPhaseLoadedQueue
+	kernel.mu.Unlock()
+
+	return sig
 }
 
 func (kernel *Kernel) setPhaseLocked(newPhase int) {
+	kernel.mu.Lock()
+	defer kernel.mu.Unlock()
 	if kernel.phase == newPhase {
 		panic("repeated phase update")
 	}