From a92e11a256d8a527d547a2772992d9d9870fa817 Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Wed, 20 Feb 2013 12:13:04 +0400
Subject: [PATCH] runtime: ensure forward progress of runtime.Gosched() for
 locked goroutines The removed code leads to the situation when M executes the
 same locked G again and again. This is https://golang.org/cl/7310096 but with
 return instead of break in the nested switch. Fixes #4820.

R=golang-dev, alex.brainman, rsc
CC=golang-dev
https://golang.org/cl/7304102
---
 src/pkg/runtime/proc.c       |  8 --------
 src/pkg/runtime/proc_test.go | 30 ++++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index f8ddf9b47e5..5c60cddf9ba 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -397,14 +397,6 @@ canaddmcpu(void)
 static void
 gput(G *gp)
 {
-	M *mp;
-
-	// If g is wired, hand it off directly.
-	if((mp = gp->lockedm) != nil && canaddmcpu()) {
-		mnextg(mp, gp);
-		return;
-	}
-
 	// If g is the idle goroutine for an m, hand it off.
 	if(gp->idlem != nil) {
 		if(gp->idlem->idleg != nil) {
diff --git a/src/pkg/runtime/proc_test.go b/src/pkg/runtime/proc_test.go
index 927bd7b816a..1f727da073c 100644
--- a/src/pkg/runtime/proc_test.go
+++ b/src/pkg/runtime/proc_test.go
@@ -46,6 +46,36 @@ func TestStopTheWorldDeadlock(t *testing.T) {
 	runtime.GOMAXPROCS(maxprocs)
 }
 
+func TestYieldProgress(t *testing.T) {
+	testYieldProgress(t, false)
+}
+
+func TestYieldLockedProgress(t *testing.T) {
+	testYieldProgress(t, true)
+}
+
+func testYieldProgress(t *testing.T, locked bool) {
+	c := make(chan bool)
+	cack := make(chan bool)
+	go func() {
+		if locked {
+			runtime.LockOSThread()
+		}
+		for {
+			select {
+			case <-c:
+				cack <- true
+				return
+			default:
+				runtime.Gosched()
+			}
+		}
+	}()
+	time.Sleep(10 * time.Millisecond)
+	c <- true
+	<-cack
+}
+
 func TestYieldLocked(t *testing.T) {
 	const N = 10
 	c := make(chan bool)