2 files changed, 29 insertions, 3 deletions
diff --git a/src/runtime/crash_test.go b/src/runtime/crash_test.go
index 69e1034ff8..52d33b8f58 100644
--- a/src/runtime/crash_test.go
+++ b/src/runtime/crash_test.go
@@ -621,7 +621,7 @@ func TestConcurrentMapWrites(t *testing.T) {
 	}
 	testenv.MustHaveGoRun(t)
 	output := runTestProg(t, "testprog", "concurrentMapWrites")
-	want := "fatal error: concurrent map writes"
+	want := "fatal error: concurrent map writes\n"
 	if !strings.HasPrefix(output, want) {
 		t.Fatalf("output does not start with %q:\n%s", want, output)
 	}
@@ -632,7 +632,7 @@ func TestConcurrentMapReadWrite(t *testing.T) {
 	}
 	testenv.MustHaveGoRun(t)
 	output := runTestProg(t, "testprog", "concurrentMapReadWrite")
-	want := "fatal error: concurrent map read and map write"
+	want := "fatal error: concurrent map read and map write\n"
 	if !strings.HasPrefix(output, want) {
 		t.Fatalf("output does not start with %q:\n%s", want, output)
 	}
@@ -643,12 +643,36 @@ func TestConcurrentMapIterateWrite(t *testing.T) {
 	}
 	testenv.MustHaveGoRun(t)
 	output := runTestProg(t, "testprog", "concurrentMapIterateWrite")
-	want := "fatal error: concurrent map iteration and map write"
+	want := "fatal error: concurrent map iteration and map write\n"
 	if !strings.HasPrefix(output, want) {
 		t.Fatalf("output does not start with %q:\n%s", want, output)
 	}
 }
 
+func TestConcurrentMapWritesIssue69447(t *testing.T) {
+	testenv.MustHaveGoRun(t)
+	exe, err := buildTestProg(t, "testprog")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 200; i++ {
+		output := runBuiltTestProg(t, exe, "concurrentMapWrites")
+		if output == "" {
+			// If we didn't detect an error, that's ok.
+			// This case makes this test not flaky like
+			// the other ones above.
+			// (More correctly, this case makes this test flaky
+			// in the other direction, in that it might not
+			// detect a problem even if there is one.)
+			continue
+		}
+		want := "fatal error: concurrent map writes\n"
+		if !strings.HasPrefix(output, want) {
+			t.Fatalf("output does not start with %q:\n%s", want, output)
+		}
+	}
+}
+
 type point struct {
 	x, y *int
 }
diff --git a/src/runtime/panic.go b/src/runtime/panic.go
index 5b62e019d9..d70d567912 100644
--- a/src/runtime/panic.go
+++ b/src/runtime/panic.go
@@ -1081,6 +1081,7 @@ func throw(s string) {
 func fatal(s string) {
 	// Everything fatal does should be recursively nosplit so it
 	// can be called even when it's unsafe to grow the stack.
+	printlock() // Prevent multiple interleaved fatal reports. See issue 69447.
 	systemstack(func() {
 		print("fatal error: ")
 		printindented(s) // logically printpanicval(s), but avoids convTstring write barrier
@@ -1088,6 +1089,7 @@ func fatal(s string) {
 	})
 
 	fatalthrow(throwTypeUser)
+	printunlock()
 }
 
 // runningPanicDefers is non-zero while running deferred functions for panic.