From: Russ Cox <rsc@golang.org>
Date: Fri, 28 Feb 2014 03:43:34 +0000 (-0500)
Subject: [release-branch.go1.2] runtime: fix data race in GC
X-Git-Tag: go1.2.1~4
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=495b91430f7914b221d7507e60b065733e2d34c4;p=gostls13.git

[release-branch.go1.2] runtime: fix data race in GC

««« CL 52090045 / 302bdb5b08b1
runtime: fix data race in GC
Fixes #5139.
Update #7065.

R=golang-codereviews, bradfitz, minux.ma
CC=golang-codereviews
https://golang.org/cl/52090045
»»»

LGTM=r
R=golang-codereviews, r
CC=golang-dev
https://golang.org/cl/69790043
---

diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 4b2108ba7a..761f128a85 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -1798,6 +1798,8 @@ runtime·memorydump(void)
 void
 runtime·gchelper(void)
 {
+	int32 nproc;
+
 	gchelperstart();
 
 	// parallel mark for over gc roots
@@ -1814,7 +1816,8 @@ runtime·gchelper(void)
 
 	runtime·parfordo(work.sweepfor);
 	bufferList[m->helpgc].busy = 0;
-	if(runtime·xadd(&work.ndone, +1) == work.nproc-1)
+	nproc = work.nproc;  // work.nproc can change right after we increment work.ndone
+	if(runtime·xadd(&work.ndone, +1) == nproc-1)
 		runtime·notewakeup(&work.alldone);
 }