From: Dmitriy Vyukov <dvyukov@google.com>
Date: Sat, 15 Jun 2013 12:07:06 +0000 (+0400)
Subject: runtime: fix race condition between GC and setGCPercent
X-Git-Tag: go1.2rc2~1239
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=94dc963b558b3d37906af53eca45c5ae807a9e84;p=gostls13.git

runtime: fix race condition between GC and setGCPercent
If first GC runs concurrently with setGCPercent,
it can overwrite gcpercent value with default.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/10242047
---

diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index a55ee49c77..4be0eeb0db 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -1974,7 +1974,10 @@ runtime·gc(int32 force)
 		return;
 
 	if(gcpercent == GcpercentUnknown) {	// first time through
-		gcpercent = readgogc();
+		runtime·lock(&runtime·mheap);
+		if(gcpercent == GcpercentUnknown)
+			gcpercent = readgogc();
+		runtime·unlock(&runtime·mheap);
 
 		p = runtime·getenv("GOGCTRACE");
 		if(p != nil)