runtime: tell race detector about reflectOffs.lock

Fixes #15832

Change-Id: I6f3f45e3c21edd0e093ecb1d8a067907863478f5
Reviewed-on: https://go-review.googlesource.com/23441Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

src/reflect/all_test.go

@@ -5722,3 +5722,18 @@ func TestTypeStrings(t *testing.T) {
 		}
 	}
 }
+
+func TestOffsetLock(t *testing.T) {
+	var wg sync.WaitGroup
+	for i := 0; i < 4; i++ {
+		i := i
+		wg.Add(1)
+		go func() {
+			for j := 0; j < 50; j++ {
+				ResolveReflectName(fmt.Sprintf("OffsetLockName:%d:%d", i, j))
+			}
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+}

src/reflect/export_test.go

@@ -109,3 +109,7 @@ func IsExported(t Type) bool {
 	n := typ.nameOff(typ.str)
 	return n.isExported()
 }
+
+func ResolveReflectName(s string) {
+	resolveReflectName(newName(s, "", "", false))
+}

src/runtime/runtime1.go

@@ -509,7 +509,7 @@ func reflect_resolveTextOff(rtype unsafe.Pointer, off int32) unsafe.Pointer {
 // reflect_addReflectOff adds a pointer to the reflection offset lookup map.
 //go:linkname reflect_addReflectOff reflect.addReflectOff
 func reflect_addReflectOff(ptr unsafe.Pointer) int32 {
-	lock(&reflectOffs.lock)
+	reflectOffsLock()
 	if reflectOffs.m == nil {
 		reflectOffs.m = make(map[int32]unsafe.Pointer)
 		reflectOffs.minv = make(map[unsafe.Pointer]int32)
@@ -522,6 +522,6 @@ func reflect_addReflectOff(ptr unsafe.Pointer) int32 {
 		reflectOffs.m[id] = ptr
 		reflectOffs.minv[ptr] = id
 	}
-	unlock(&reflectOffs.lock)
+	reflectOffsUnlock()
 	return id
 }

src/runtime/type.go

@@ -169,6 +169,20 @@ var reflectOffs struct {
 	minv map[unsafe.Pointer]int32
 }
 
+func reflectOffsLock() {
+	lock(&reflectOffs.lock)
+	if raceenabled {
+		raceacquire(unsafe.Pointer(&reflectOffs.lock))
+	}
+}
+
+func reflectOffsUnlock() {
+	if raceenabled {
+		racerelease(unsafe.Pointer(&reflectOffs.lock))
+	}
+	unlock(&reflectOffs.lock)
+}
+
 func resolveNameOff(ptrInModule unsafe.Pointer, off nameOff) name {
 	if off == 0 {
 		return name{}
@@ -182,9 +196,9 @@ func resolveNameOff(ptrInModule unsafe.Pointer, off nameOff) name {
 		}
 	}
 	if md == nil {
-		lock(&reflectOffs.lock)
+		reflectOffsLock()
 		res, found := reflectOffs.m[int32(off)]
-		unlock(&reflectOffs.lock)
+		reflectOffsUnlock()
 		if !found {
 			println("runtime: nameOff", hex(off), "base", hex(base), "not in ranges:")
 			for next := &firstmoduledata; next != nil; next = next.next {
@@ -219,9 +233,9 @@ func (t *_type) typeOff(off typeOff) *_type {
 		}
 	}
 	if md == nil {
-		lock(&reflectOffs.lock)
+		reflectOffsLock()
 		res := reflectOffs.m[int32(off)]
-		unlock(&reflectOffs.lock)
+		reflectOffsUnlock()
 		if res == nil {
 			println("runtime: typeOff", hex(off), "base", hex(base), "not in ranges:")
 			for next := &firstmoduledata; next != nil; next = next.next {
@@ -252,9 +266,9 @@ func (t *_type) textOff(off textOff) unsafe.Pointer {
 		}
 	}
 	if md == nil {
-		lock(&reflectOffs.lock)
+		reflectOffsLock()
 		res := reflectOffs.m[int32(off)]
-		unlock(&reflectOffs.lock)
+		reflectOffsUnlock()
 		if res == nil {
 			println("runtime: textOff", hex(off), "base", hex(base), "not in ranges:")
 			for next := &firstmoduledata; next != nil; next = next.next {