runtime: in getTraceback, set gp->m before gogo

    
    Currently, when collecting a traceback for another goroutine,
    getTraceback calls gogo(gp) switching to gp, which will resume in
    mcall, which will call gtraceback, which will set up gp->m. There
    is a gap between setting the current running g to gp and setting
    gp->m. If a profiling signal arrives in between, sigtramp will
    see a non-nil gp with a nil m, and will seg fault. Fix this by
    setting up gp->m first.
    
    Fixes golang/go#29448.
    
    Reviewed-on: https://go-review.googlesource.com/c/156038

From-SVN: r267658

1 files changed, 35 insertions, 0 deletions

diff --git a/libgo/go/runtime/pprof/pprof_test.go b/libgo/go/runtime/pprof/pprof_test.go
index 74a7777..fd05a04 100644
--- a/libgo/go/runtime/pprof/pprof_test.go
+++ b/libgo/go/runtime/pprof/pprof_test.go
@@ -946,3 +946,38 @@ func TestAtomicLoadStore64(t *testing.T) {
 	atomic.StoreUint64(&flag, 1)
 	<-done
 }
+
+func TestTracebackAll(t *testing.T) {
+	// With gccgo, if a profiling signal arrives at the wrong time
+	// during traceback, it may crash or hang. See issue #29448.
+	f, err := ioutil.TempFile("", "proftraceback")
+	if err != nil {
+		t.Fatalf("TempFile: %v", err)
+	}
+	defer os.Remove(f.Name())
+	defer f.Close()
+
+	if err := StartCPUProfile(f); err != nil {
+		t.Fatal(err)
+	}
+	defer StopCPUProfile()
+
+	ch := make(chan int)
+	defer close(ch)
+
+	count := 10
+	for i := 0; i < count; i++ {
+		go func() {
+			<-ch // block
+		}()
+	}
+
+	N := 10000
+	if testing.Short() {
+		N = 500
+	}
+	buf := make([]byte, 10*1024)
+	for i := 0; i < N; i++ {
+		runtime.Stack(buf, true)
+	}
+}