runtime: never show system goroutines in traceback

Fixes #9791

g.issystem flag setup races with other code wherever we set it.
Even if we set both in parent goroutine and in the system goroutine,
it is still possible that some other goroutine crashes
before the flag is set. We could pass issystem flag to newproc1,
but we start all goroutines with go nowadays.

Instead look at g.startpc to distinguish system goroutines (similar to topofstack).

Change-Id: Ia3467968dee27fa07d9fecedd4c2b00928f26645
Reviewed-on: https://go-review.googlesource.com/4113
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 22 insertions, 1 deletions

diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
index 6c87d7e2e4..8c31c5abad 100644
--- a/src/runtime/traceback.go
+++ b/src/runtime/traceback.go
@@ -39,6 +39,11 @@ var (
 	mstartPC             uintptr
 	rt0_goPC             uintptr
 	sigpanicPC           uintptr
+	runfinqPC            uintptr
+	backgroundgcPC       uintptr
+	bgsweepPC            uintptr
+	forcegchelperPC      uintptr
+	timerprocPC          uintptr
 	systemstack_switchPC uintptr
 
 	externalthreadhandlerp uintptr // initialized elsewhere
@@ -56,6 +61,11 @@ func tracebackinit() {
 	mstartPC = funcPC(mstart)
 	rt0_goPC = funcPC(rt0_go)
 	sigpanicPC = funcPC(sigpanic)
+	runfinqPC = funcPC(runfinq)
+	backgroundgcPC = funcPC(backgroundgc)
+	bgsweepPC = funcPC(bgsweep)
+	forcegchelperPC = funcPC(forcegchelper)
+	timerprocPC = funcPC(timerproc)
 	systemstack_switchPC = funcPC(systemstack_switch)
 }
 
@@ -606,7 +616,7 @@ func tracebackothers(me *g) {
 
 	lock(&allglock)
 	for _, gp := range allgs {
-		if gp == me || gp == g.m.curg || readgstatus(gp) == _Gdead || gp.issystem && level < 2 {
+		if gp == me || gp == g.m.curg || readgstatus(gp) == _Gdead || isSystemGoroutine(gp) && level < 2 {
 			continue
 		}
 		print("\n")
@@ -631,3 +641,14 @@ func topofstack(f *_func) bool {
 		pc == rt0_goPC ||
 		externalthreadhandlerp != 0 && pc == externalthreadhandlerp
 }
+
+// isSystemGoroutine returns true if the goroutine g must be omitted in
+// stack dumps and deadlock detector.
+func isSystemGoroutine(gp *g) bool {
+	pc := gp.startpc
+	return pc == runfinqPC && !fingRunning ||
+		pc == backgroundgcPC ||
+		pc == bgsweepPC ||
+		pc == forcegchelperPC ||
+		pc == timerprocPC
+}