This libgo patch by Cherry Zhang moves setting p->m from gtraceback to
getTraceback. 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. This patch fixes this by
setting up gp->m first. This fixes https://golang.org/issue/29448.
Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu. Committed
to mainline.
Ian
Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE (revision 267590)
+++ gcc/go/gofrontend/MERGE (working copy)
@@ -1,4 +1,4 @@
-2ce291eaee427799bfcde256929dab89e0ab61eb
+c257303eaef143663216e483857d5b259e05753f
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.
Index: libgo/go/runtime/pprof/pprof_test.go
===================================================================
--- libgo/go/runtime/pprof/pprof_test.go (revision 267580)
+++ libgo/go/runtime/pprof/pprof_test.go (working copy)
@@ -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)
+ }
+}
Index: libgo/runtime/proc.c
===================================================================
--- libgo/runtime/proc.c (revision 267580)
+++ libgo/runtime/proc.c (working copy)
@@ -442,6 +442,11 @@ void getTraceback(G*, G*) __asm__(GOSYM_
// 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 @@ void getTraceback(G* me, G* gp)
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 @@ void
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);
}
