all: Remove potentially problematic errors from panics (fixes #5839) (#5912)

cmd/syncthing/blockprof.go

@@ -22,11 +22,15 @@ func init() {
 			panic("Couldn't find block profiler")
 		}
 		l.Debugln("Starting block profiling")
-		go saveBlockingProfiles(profiler)
+		go func() {
+			err := saveBlockingProfiles(profiler) // Only returns on error
+			l.Warnln("Block profiler failed:", err)
+			panic("Block profiler failed")
+		}()
 	}
 }
 
-func saveBlockingProfiles(profiler *pprof.Profile) {
+func saveBlockingProfiles(profiler *pprof.Profile) error {
 	runtime.SetBlockProfileRate(1)
 
 	t0 := time.Now()
@@ -35,16 +39,16 @@ func saveBlockingProfiles(profiler *pprof.Profile) {
 
 		fd, err := os.Create(fmt.Sprintf("block-%05d-%07d.pprof", syscall.Getpid(), startms))
 		if err != nil {
-			panic(err)
+			return err
 		}
 		err = profiler.WriteTo(fd, 0)
 		if err != nil {
-			panic(err)
+			return err
 		}
 		err = fd.Close()
 		if err != nil {
-			panic(err)
+			return err
 		}
-
 	}
+	return nil
 }

cmd/syncthing/heapprof.go

@@ -23,11 +23,15 @@ func init() {
 			rate = i
 		}
 		l.Debugln("Starting heap profiling")
-		go saveHeapProfiles(rate)
+		go func() {
+			err := saveHeapProfiles(rate) // Only returns on error
+			l.Warnln("Heap profiler failed:", err)
+			panic("Heap profiler failed")
+		}()
 	}
 }
 
-func saveHeapProfiles(rate int) {
+func saveHeapProfiles(rate int) error {
 	runtime.MemProfileRate = rate
 	var memstats, prevMemstats runtime.MemStats
 
@@ -38,21 +42,21 @@ func saveHeapProfiles(rate int) {
 		if memstats.HeapInuse > prevMemstats.HeapInuse {
 			fd, err := os.Create(name + ".tmp")
 			if err != nil {
-				panic(err)
+				return err
 			}
 			err = pprof.WriteHeapProfile(fd)
 			if err != nil {
-				panic(err)
+				return err
 			}
 			err = fd.Close()
 			if err != nil {
-				panic(err)
+				return err
 			}
 
 			os.Remove(name) // Error deliberately ignored
 			err = os.Rename(name+".tmp", name)
 			if err != nil {
-				panic(err)
+				return err
 			}
 
 			prevMemstats = memstats

cmd/syncthing/monitor.go

@@ -102,7 +102,8 @@ func monitorMain(runtimeOptions RuntimeOptions) {
 		l.Infoln("Starting syncthing")
 		err = cmd.Start()
 		if err != nil {
-			panic(err)
+			l.Warnln("Error starting the main Syncthing process:", err)
+			panic("Error starting the main Syncthing process")
 		}
 
 		stdoutMut.Lock()