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.
Change-Id: Ic2c65e2692c48b08279079408d47d07e16375025
Reviewed-on: https://go-review.googlesource.com/c/156038
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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 @@
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)
+ }
+}
diff --git a/libgo/runtime/proc.c b/libgo/runtime/proc.c
index 99b2cb1..4004df4 100644
--- a/libgo/runtime/proc.c
+++ b/libgo/runtime/proc.c
@@ -442,6 +442,11 @@
// goroutine stored in the traceback field, which is me.
void getTraceback(G* me, G* gp)
{
+ M* holdm;
+
+ holdm = gp->m;
+ gp->m = me->m;
+
#ifdef USING_SPLIT_STACK
__splitstack_getcontext((void*)(&me->stackcontext[0]));
#endif
@@ -450,6 +455,8 @@
if (gp->traceback != 0) {
runtime_gogo(gp);
}
+
+ gp->m = holdm;
}
// Do a stack trace of gp, and then restore the context to
@@ -459,17 +466,11 @@
gtraceback(G* gp)
{
Traceback* traceback;
- M* holdm;
traceback = (Traceback*)gp->traceback;
gp->traceback = 0;
- holdm = gp->m;
- if(holdm != nil && holdm != g->m)
- runtime_throw("gtraceback: m is not nil");
- gp->m = traceback->gp->m;
traceback->c = runtime_callers(1, traceback->locbuf,
sizeof traceback->locbuf / sizeof traceback->locbuf[0], false);
- gp->m = holdm;
runtime_gogo(traceback->gp);
}
